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<div class="section" id="module-sys">
<span id="sys-system-specific-parameters-and-functions"></span><h1>29.1. <a class="reference internal" href="#module-sys" title="sys: Access system-specific parameters and functions."><code class="xref py py-mod docutils literal"><span class="pre">sys</span></code></a> — System-specific parameters and functions<a class="headerlink" href="#module-sys" title="Permalink to this headline">¶</a></h1>
<hr class="docutils" />
<p>This module provides access to some variables used or maintained by the
interpreter and to functions that interact strongly with the interpreter. It is
always available.</p>
<dl class="data">
<dt id="sys.abiflags">
<code class="descclassname">sys.</code><code class="descname">abiflags</code><a class="headerlink" href="#sys.abiflags" title="Permalink to this definition">¶</a></dt>
<dd><p>On POSIX systems where Python was built with the standard <code class="docutils literal"><span class="pre">configure</span></code>
script, this contains the ABI flags as specified by <span class="target" id="index-0"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3149"><strong>PEP 3149</strong></a>.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.2.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.argv">
<code class="descclassname">sys.</code><code class="descname">argv</code><a class="headerlink" href="#sys.argv" title="Permalink to this definition">¶</a></dt>
<dd><p>The list of command line arguments passed to a Python script. <code class="docutils literal"><span class="pre">argv[0]</span></code> is the
script name (it is operating system dependent whether this is a full pathname or
not). If the command was executed using the <a class="reference internal" href="../using/cmdline.html#cmdoption-c"><code class="xref std std-option docutils literal"><span class="pre">-c</span></code></a> command line option to
the interpreter, <code class="docutils literal"><span class="pre">argv[0]</span></code> is set to the string <code class="docutils literal"><span class="pre">'-c'</span></code>. If no script name
was passed to the Python interpreter, <code class="docutils literal"><span class="pre">argv[0]</span></code> is the empty string.</p>
<p>To loop over the standard input, or the list of files given on the
command line, see the <a class="reference internal" href="fileinput.html#module-fileinput" title="fileinput: Loop over standard input or a list of files."><code class="xref py py-mod docutils literal"><span class="pre">fileinput</span></code></a> module.</p>
</dd></dl>
<dl class="data">
<dt id="sys.base_exec_prefix">
<code class="descclassname">sys.</code><code class="descname">base_exec_prefix</code><a class="headerlink" href="#sys.base_exec_prefix" title="Permalink to this definition">¶</a></dt>
<dd><p>Set during Python startup, before <code class="docutils literal"><span class="pre">site.py</span></code> is run, to the same value as
<a class="reference internal" href="#sys.exec_prefix" title="sys.exec_prefix"><code class="xref py py-data docutils literal"><span class="pre">exec_prefix</span></code></a>. If not running in a
<a class="reference internal" href="venv.html#venv-def"><span>virtual environment</span></a>, the values will stay the same; if
<code class="docutils literal"><span class="pre">site.py</span></code> finds that a virtual environment is in use, the values of
<a class="reference internal" href="#sys.prefix" title="sys.prefix"><code class="xref py py-data docutils literal"><span class="pre">prefix</span></code></a> and <a class="reference internal" href="#sys.exec_prefix" title="sys.exec_prefix"><code class="xref py py-data docutils literal"><span class="pre">exec_prefix</span></code></a> will be changed to point to the
virtual environment, whereas <a class="reference internal" href="#sys.base_prefix" title="sys.base_prefix"><code class="xref py py-data docutils literal"><span class="pre">base_prefix</span></code></a> and
<a class="reference internal" href="#sys.base_exec_prefix" title="sys.base_exec_prefix"><code class="xref py py-data docutils literal"><span class="pre">base_exec_prefix</span></code></a> will remain pointing to the base Python
installation (the one which the virtual environment was created from).</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.3.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.base_prefix">
<code class="descclassname">sys.</code><code class="descname">base_prefix</code><a class="headerlink" href="#sys.base_prefix" title="Permalink to this definition">¶</a></dt>
<dd><p>Set during Python startup, before <code class="docutils literal"><span class="pre">site.py</span></code> is run, to the same value as
<a class="reference internal" href="#sys.prefix" title="sys.prefix"><code class="xref py py-data docutils literal"><span class="pre">prefix</span></code></a>. If not running in a <a class="reference internal" href="venv.html#venv-def"><span>virtual environment</span></a>, the values
will stay the same; if <code class="docutils literal"><span class="pre">site.py</span></code> finds that a virtual environment is in
use, the values of <a class="reference internal" href="#sys.prefix" title="sys.prefix"><code class="xref py py-data docutils literal"><span class="pre">prefix</span></code></a> and <a class="reference internal" href="#sys.exec_prefix" title="sys.exec_prefix"><code class="xref py py-data docutils literal"><span class="pre">exec_prefix</span></code></a> will be changed to
point to the virtual environment, whereas <a class="reference internal" href="#sys.base_prefix" title="sys.base_prefix"><code class="xref py py-data docutils literal"><span class="pre">base_prefix</span></code></a> and
<a class="reference internal" href="#sys.base_exec_prefix" title="sys.base_exec_prefix"><code class="xref py py-data docutils literal"><span class="pre">base_exec_prefix</span></code></a> will remain pointing to the base Python
installation (the one which the virtual environment was created from).</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.3.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.byteorder">
<code class="descclassname">sys.</code><code class="descname">byteorder</code><a class="headerlink" href="#sys.byteorder" title="Permalink to this definition">¶</a></dt>
<dd><p>An indicator of the native byte order. This will have the value <code class="docutils literal"><span class="pre">'big'</span></code> on
big-endian (most-significant byte first) platforms, and <code class="docutils literal"><span class="pre">'little'</span></code> on
little-endian (least-significant byte first) platforms.</p>
</dd></dl>
<dl class="data">
<dt id="sys.builtin_module_names">
<code class="descclassname">sys.</code><code class="descname">builtin_module_names</code><a class="headerlink" href="#sys.builtin_module_names" title="Permalink to this definition">¶</a></dt>
<dd><p>A tuple of strings giving the names of all modules that are compiled into this
Python interpreter. (This information is not available in any other way —
<code class="docutils literal"><span class="pre">modules.keys()</span></code> only lists the imported modules.)</p>
</dd></dl>
<dl class="function">
<dt id="sys.call_tracing">
<code class="descclassname">sys.</code><code class="descname">call_tracing</code><span class="sig-paren">(</span><em>func</em>, <em>args</em><span class="sig-paren">)</span><a class="headerlink" href="#sys.call_tracing" title="Permalink to this definition">¶</a></dt>
<dd><p>Call <code class="docutils literal"><span class="pre">func(*args)</span></code>, while tracing is enabled. The tracing state is saved,
and restored afterwards. This is intended to be called from a debugger from
a checkpoint, to recursively debug some other code.</p>
</dd></dl>
<dl class="data">
<dt id="sys.copyright">
<code class="descclassname">sys.</code><code class="descname">copyright</code><a class="headerlink" href="#sys.copyright" title="Permalink to this definition">¶</a></dt>
<dd><p>A string containing the copyright pertaining to the Python interpreter.</p>
</dd></dl>
<dl class="function">
<dt id="sys._clear_type_cache">
<code class="descclassname">sys.</code><code class="descname">_clear_type_cache</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys._clear_type_cache" title="Permalink to this definition">¶</a></dt>
<dd><p>Clear the internal type cache. The type cache is used to speed up attribute
and method lookups. Use the function <em>only</em> to drop unnecessary references
during reference leak debugging.</p>
<p>This function should be used for internal and specialized purposes only.</p>
</dd></dl>
<dl class="function">
<dt id="sys._current_frames">
<code class="descclassname">sys.</code><code class="descname">_current_frames</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys._current_frames" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a dictionary mapping each thread’s identifier to the topmost stack frame
currently active in that thread at the time the function is called. Note that
functions in the <a class="reference internal" href="traceback.html#module-traceback" title="traceback: Print or retrieve a stack traceback."><code class="xref py py-mod docutils literal"><span class="pre">traceback</span></code></a> module can build the call stack given such a
frame.</p>
<p>This is most useful for debugging deadlock: this function does not require the
deadlocked threads’ cooperation, and such threads’ call stacks are frozen for as
long as they remain deadlocked. The frame returned for a non-deadlocked thread
may bear no relationship to that thread’s current activity by the time calling
code examines the frame.</p>
<p>This function should be used for internal and specialized purposes only.</p>
</dd></dl>
<dl class="function">
<dt id="sys._debugmallocstats">
<code class="descclassname">sys.</code><code class="descname">_debugmallocstats</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys._debugmallocstats" title="Permalink to this definition">¶</a></dt>
<dd><p>Print low-level information to stderr about the state of CPython’s memory
allocator.</p>
<p>If Python is configured –with-pydebug, it also performs some expensive
internal consistency checks.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.3.</span></p>
</div>
<div class="impl-detail compound">
<p><strong>CPython implementation detail:</strong> This function is specific to CPython. The exact output format is not
defined here, and may change.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.dllhandle">
<code class="descclassname">sys.</code><code class="descname">dllhandle</code><a class="headerlink" href="#sys.dllhandle" title="Permalink to this definition">¶</a></dt>
<dd><p>Integer specifying the handle of the Python DLL. Availability: Windows.</p>
</dd></dl>
<dl class="function">
<dt id="sys.displayhook">
<code class="descclassname">sys.</code><code class="descname">displayhook</code><span class="sig-paren">(</span><em>value</em><span class="sig-paren">)</span><a class="headerlink" href="#sys.displayhook" title="Permalink to this definition">¶</a></dt>
<dd><p>If <em>value</em> is not <code class="docutils literal"><span class="pre">None</span></code>, this function prints <code class="docutils literal"><span class="pre">repr(value)</span></code> to
<code class="docutils literal"><span class="pre">sys.stdout</span></code>, and saves <em>value</em> in <code class="docutils literal"><span class="pre">builtins._</span></code>. If <code class="docutils literal"><span class="pre">repr(value)</span></code> is
not encodable to <code class="docutils literal"><span class="pre">sys.stdout.encoding</span></code> with <code class="docutils literal"><span class="pre">sys.stdout.errors</span></code> error
handler (which is probably <code class="docutils literal"><span class="pre">'strict'</span></code>), encode it to
<code class="docutils literal"><span class="pre">sys.stdout.encoding</span></code> with <code class="docutils literal"><span class="pre">'backslashreplace'</span></code> error handler.</p>
<p><code class="docutils literal"><span class="pre">sys.displayhook</span></code> is called on the result of evaluating an <a class="reference internal" href="../glossary.html#term-expression"><span class="xref std std-term">expression</span></a>
entered in an interactive Python session. The display of these values can be
customized by assigning another one-argument function to <code class="docutils literal"><span class="pre">sys.displayhook</span></code>.</p>
<p>Pseudo-code:</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">displayhook</span><span class="p">(</span><span class="n">value</span><span class="p">):</span>
<span class="k">if</span> <span class="n">value</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span>
<span class="k">return</span>
<span class="c1"># Set '_' to None to avoid recursion</span>
<span class="n">builtins</span><span class="o">.</span><span class="n">_</span> <span class="o">=</span> <span class="kc">None</span>
<span class="n">text</span> <span class="o">=</span> <span class="nb">repr</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">text</span><span class="p">)</span>
<span class="k">except</span> <span class="ne">UnicodeEncodeError</span><span class="p">:</span>
<span class="nb">bytes</span> <span class="o">=</span> <span class="n">text</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="o">.</span><span class="n">encoding</span><span class="p">,</span> <span class="s1">'backslashreplace'</span><span class="p">)</span>
<span class="k">if</span> <span class="nb">hasattr</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="p">,</span> <span class="s1">'buffer'</span><span class="p">):</span>
<span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="o">.</span><span class="n">buffer</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="nb">bytes</span><span class="p">)</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">text</span> <span class="o">=</span> <span class="nb">bytes</span><span class="o">.</span><span class="n">decode</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="o">.</span><span class="n">encoding</span><span class="p">,</span> <span class="s1">'strict'</span><span class="p">)</span>
<span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">text</span><span class="p">)</span>
<span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s2">"</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span>
<span class="n">builtins</span><span class="o">.</span><span class="n">_</span> <span class="o">=</span> <span class="n">value</span>
</pre></div>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.2: </span>Use <code class="docutils literal"><span class="pre">'backslashreplace'</span></code> error handler on <a class="reference internal" href="exceptions.html#UnicodeEncodeError" title="UnicodeEncodeError"><code class="xref py py-exc docutils literal"><span class="pre">UnicodeEncodeError</span></code></a>.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.dont_write_bytecode">
<code class="descclassname">sys.</code><code class="descname">dont_write_bytecode</code><a class="headerlink" href="#sys.dont_write_bytecode" title="Permalink to this definition">¶</a></dt>
<dd><p>If this is true, Python won’t try to write <code class="docutils literal"><span class="pre">.pyc</span></code> files on the
import of source modules. This value is initially set to <code class="docutils literal"><span class="pre">True</span></code> or
<code class="docutils literal"><span class="pre">False</span></code> depending on the <a class="reference internal" href="../using/cmdline.html#cmdoption-B"><code class="xref std std-option docutils literal"><span class="pre">-B</span></code></a> command line option and the
<span class="target" id="index-1"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONDONTWRITEBYTECODE"><code class="xref std std-envvar docutils literal"><span class="pre">PYTHONDONTWRITEBYTECODE</span></code></a> environment variable, but you can set it
yourself to control bytecode file generation.</p>
</dd></dl>
<dl class="function">
<dt id="sys.excepthook">
<code class="descclassname">sys.</code><code class="descname">excepthook</code><span class="sig-paren">(</span><em>type</em>, <em>value</em>, <em>traceback</em><span class="sig-paren">)</span><a class="headerlink" href="#sys.excepthook" title="Permalink to this definition">¶</a></dt>
<dd><p>This function prints out a given traceback and exception to <code class="docutils literal"><span class="pre">sys.stderr</span></code>.</p>
<p>When an exception is raised and uncaught, the interpreter calls
<code class="docutils literal"><span class="pre">sys.excepthook</span></code> with three arguments, the exception class, exception
instance, and a traceback object. In an interactive session this happens just
before control is returned to the prompt; in a Python program this happens just
before the program exits. The handling of such top-level exceptions can be
customized by assigning another three-argument function to <code class="docutils literal"><span class="pre">sys.excepthook</span></code>.</p>
</dd></dl>
<dl class="data">
<dt id="sys.__displayhook__">
<code class="descclassname">sys.</code><code class="descname">__displayhook__</code><a class="headerlink" href="#sys.__displayhook__" title="Permalink to this definition">¶</a></dt>
<dt id="sys.__excepthook__">
<code class="descclassname">sys.</code><code class="descname">__excepthook__</code><a class="headerlink" href="#sys.__excepthook__" title="Permalink to this definition">¶</a></dt>
<dd><p>These objects contain the original values of <code class="docutils literal"><span class="pre">displayhook</span></code> and <code class="docutils literal"><span class="pre">excepthook</span></code>
at the start of the program. They are saved so that <code class="docutils literal"><span class="pre">displayhook</span></code> and
<code class="docutils literal"><span class="pre">excepthook</span></code> can be restored in case they happen to get replaced with broken
objects.</p>
</dd></dl>
<dl class="function">
<dt id="sys.exc_info">
<code class="descclassname">sys.</code><code class="descname">exc_info</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.exc_info" title="Permalink to this definition">¶</a></dt>
<dd><p>This function returns a tuple of three values that give information about the
exception that is currently being handled. The information returned is specific
both to the current thread and to the current stack frame. If the current stack
frame is not handling an exception, the information is taken from the calling
stack frame, or its caller, and so on until a stack frame is found that is
handling an exception. Here, “handling an exception” is defined as “executing
an except clause.” For any stack frame, only information about the exception
being currently handled is accessible.</p>
<p id="index-2">If no exception is being handled anywhere on the stack, a tuple containing
three <code class="docutils literal"><span class="pre">None</span></code> values is returned. Otherwise, the values returned are
<code class="docutils literal"><span class="pre">(type,</span> <span class="pre">value,</span> <span class="pre">traceback)</span></code>. Their meaning is: <em>type</em> gets the type of the
exception being handled (a subclass of <a class="reference internal" href="exceptions.html#BaseException" title="BaseException"><code class="xref py py-exc docutils literal"><span class="pre">BaseException</span></code></a>); <em>value</em> gets
the exception instance (an instance of the exception type); <em>traceback</em> gets
a traceback object (see the Reference Manual) which encapsulates the call
stack at the point where the exception originally occurred.</p>
</dd></dl>
<dl class="data">
<dt id="sys.exec_prefix">
<code class="descclassname">sys.</code><code class="descname">exec_prefix</code><a class="headerlink" href="#sys.exec_prefix" title="Permalink to this definition">¶</a></dt>
<dd><p>A string giving the site-specific directory prefix where the platform-dependent
Python files are installed; by default, this is also <code class="docutils literal"><span class="pre">'/usr/local'</span></code>. This can
be set at build time with the <code class="docutils literal"><span class="pre">--exec-prefix</span></code> argument to the
<strong class="program">configure</strong> script. Specifically, all configuration files (e.g. the
<code class="file docutils literal"><span class="pre">pyconfig.h</span></code> header file) are installed in the directory
<code class="file docutils literal"><em><span class="pre">exec_prefix</span></em><span class="pre">/lib/python</span><em><span class="pre">X.Y</span></em><span class="pre">/config</span></code>, and shared library modules are
installed in <code class="file docutils literal"><em><span class="pre">exec_prefix</span></em><span class="pre">/lib/python</span><em><span class="pre">X.Y</span></em><span class="pre">/lib-dynload</span></code>, where <em>X.Y</em>
is the version number of Python, for example <code class="docutils literal"><span class="pre">3.2</span></code>.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">If a <a class="reference internal" href="venv.html#venv-def"><span>virtual environment</span></a> is in effect, this
value will be changed in <code class="docutils literal"><span class="pre">site.py</span></code> to point to the virtual environment.
The value for the Python installation will still be available, via
<a class="reference internal" href="#sys.base_exec_prefix" title="sys.base_exec_prefix"><code class="xref py py-data docutils literal"><span class="pre">base_exec_prefix</span></code></a>.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.executable">
<code class="descclassname">sys.</code><code class="descname">executable</code><a class="headerlink" href="#sys.executable" title="Permalink to this definition">¶</a></dt>
<dd><p>A string giving the absolute path of the executable binary for the Python
interpreter, on systems where this makes sense. If Python is unable to retrieve
the real path to its executable, <a class="reference internal" href="#sys.executable" title="sys.executable"><code class="xref py py-data docutils literal"><span class="pre">sys.executable</span></code></a> will be an empty string
or <code class="docutils literal"><span class="pre">None</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="sys.exit">
<code class="descclassname">sys.</code><code class="descname">exit</code><span class="sig-paren">(</span><span class="optional">[</span><em>arg</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.exit" title="Permalink to this definition">¶</a></dt>
<dd><p>Exit from Python. This is implemented by raising the <a class="reference internal" href="exceptions.html#SystemExit" title="SystemExit"><code class="xref py py-exc docutils literal"><span class="pre">SystemExit</span></code></a>
exception, so cleanup actions specified by finally clauses of <a class="reference internal" href="../reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal"><span class="pre">try</span></code></a>
statements are honored, and it is possible to intercept the exit attempt at
an outer level.</p>
<p>The optional argument <em>arg</em> can be an integer giving the exit status
(defaulting to zero), or another type of object. If it is an integer, zero
is considered “successful termination” and any nonzero value is considered
“abnormal termination” by shells and the like. Most systems require it to be
in the range 0–127, and produce undefined results otherwise. Some systems
have a convention for assigning specific meanings to specific exit codes, but
these are generally underdeveloped; Unix programs generally use 2 for command
line syntax errors and 1 for all other kind of errors. If another type of
object is passed, <code class="docutils literal"><span class="pre">None</span></code> is equivalent to passing zero, and any other
object is printed to <a class="reference internal" href="#sys.stderr" title="sys.stderr"><code class="xref py py-data docutils literal"><span class="pre">stderr</span></code></a> and results in an exit code of 1. In
particular, <code class="docutils literal"><span class="pre">sys.exit("some</span> <span class="pre">error</span> <span class="pre">message")</span></code> is a quick way to exit a
program when an error occurs.</p>
<p>Since <a class="reference internal" href="constants.html#exit" title="exit"><code class="xref py py-func docutils literal"><span class="pre">exit()</span></code></a> ultimately “only” raises an exception, it will only exit
the process when called from the main thread, and the exception is not
intercepted.</p>
</dd></dl>
<dl class="data">
<dt id="sys.flags">
<code class="descclassname">sys.</code><code class="descname">flags</code><a class="headerlink" href="#sys.flags" title="Permalink to this definition">¶</a></dt>
<dd><p>The <a class="reference internal" href="../glossary.html#term-struct-sequence"><span class="xref std std-term">struct sequence</span></a> <em>flags</em> exposes the status of command line
flags. The attributes are read only.</p>
<table border="1" class="docutils">
<colgroup>
<col width="50%" />
<col width="50%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">attribute</th>
<th class="head">flag</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">debug</span></code></td>
<td><a class="reference internal" href="../using/cmdline.html#cmdoption-d"><code class="xref std std-option docutils literal"><span class="pre">-d</span></code></a></td>
</tr>
<tr class="row-odd"><td><a class="reference internal" href="inspect.html#module-inspect" title="inspect: Extract information and source code from live objects."><code class="xref py py-const docutils literal"><span class="pre">inspect</span></code></a></td>
<td><a class="reference internal" href="../using/cmdline.html#cmdoption-i"><code class="xref std std-option docutils literal"><span class="pre">-i</span></code></a></td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">interactive</span></code></td>
<td><a class="reference internal" href="../using/cmdline.html#cmdoption-i"><code class="xref std std-option docutils literal"><span class="pre">-i</span></code></a></td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">optimize</span></code></td>
<td><a class="reference internal" href="../using/cmdline.html#cmdoption-O"><code class="xref std std-option docutils literal"><span class="pre">-O</span></code></a> or <a class="reference internal" href="../using/cmdline.html#cmdoption-OO"><code class="xref std std-option docutils literal"><span class="pre">-OO</span></code></a></td>
</tr>
<tr class="row-even"><td><a class="reference internal" href="#sys.dont_write_bytecode" title="sys.dont_write_bytecode"><code class="xref py py-const docutils literal"><span class="pre">dont_write_bytecode</span></code></a></td>
<td><a class="reference internal" href="../using/cmdline.html#cmdoption-B"><code class="xref std std-option docutils literal"><span class="pre">-B</span></code></a></td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">no_user_site</span></code></td>
<td><a class="reference internal" href="../using/cmdline.html#cmdoption-s"><code class="xref std std-option docutils literal"><span class="pre">-s</span></code></a></td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">no_site</span></code></td>
<td><a class="reference internal" href="../using/cmdline.html#cmdoption-S"><code class="xref std std-option docutils literal"><span class="pre">-S</span></code></a></td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">ignore_environment</span></code></td>
<td><a class="reference internal" href="../using/cmdline.html#cmdoption-E"><code class="xref std std-option docutils literal"><span class="pre">-E</span></code></a></td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">verbose</span></code></td>
<td><a class="reference internal" href="../using/cmdline.html#cmdoption-v"><code class="xref std std-option docutils literal"><span class="pre">-v</span></code></a></td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">bytes_warning</span></code></td>
<td><a class="reference internal" href="../using/cmdline.html#cmdoption-b"><code class="xref std std-option docutils literal"><span class="pre">-b</span></code></a></td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">quiet</span></code></td>
<td><a class="reference internal" href="../using/cmdline.html#cmdoption-q"><code class="xref std std-option docutils literal"><span class="pre">-q</span></code></a></td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">hash_randomization</span></code></td>
<td><a class="reference internal" href="../using/cmdline.html#cmdoption-R"><code class="xref std std-option docutils literal"><span class="pre">-R</span></code></a></td>
</tr>
</tbody>
</table>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.2: </span>Added <code class="docutils literal"><span class="pre">quiet</span></code> attribute for the new <a class="reference internal" href="../using/cmdline.html#cmdoption-q"><code class="xref std std-option docutils literal"><span class="pre">-q</span></code></a> flag.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.2.3: </span>The <code class="docutils literal"><span class="pre">hash_randomization</span></code> attribute.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3: </span>Removed obsolete <code class="docutils literal"><span class="pre">division_warning</span></code> attribute.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.float_info">
<code class="descclassname">sys.</code><code class="descname">float_info</code><a class="headerlink" href="#sys.float_info" title="Permalink to this definition">¶</a></dt>
<dd><p>A <a class="reference internal" href="../glossary.html#term-struct-sequence"><span class="xref std std-term">struct sequence</span></a> holding information about the float type. It
contains low level information about the precision and internal
representation. The values correspond to the various floating-point
constants defined in the standard header file <code class="file docutils literal"><span class="pre">float.h</span></code> for the ‘C’
programming language; see section 5.2.4.2.2 of the 1999 ISO/IEC C standard
<a class="reference internal" href="#c99" id="id1">[C99]</a>, ‘Characteristics of floating types’, for details.</p>
<table border="1" class="docutils">
<colgroup>
<col width="24%" />
<col width="18%" />
<col width="57%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">attribute</th>
<th class="head">float.h macro</th>
<th class="head">explanation</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">epsilon</span></code></td>
<td>DBL_EPSILON</td>
<td>difference between 1 and the least value greater
than 1 that is representable as a float</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">dig</span></code></td>
<td>DBL_DIG</td>
<td>maximum number of decimal digits that can be
faithfully represented in a float; see below</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">mant_dig</span></code></td>
<td>DBL_MANT_DIG</td>
<td>float precision: the number of base-<code class="docutils literal"><span class="pre">radix</span></code>
digits in the significand of a float</td>
</tr>
<tr class="row-odd"><td><a class="reference internal" href="functions.html#max" title="max"><code class="xref py py-const docutils literal"><span class="pre">max</span></code></a></td>
<td>DBL_MAX</td>
<td>maximum representable finite float</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">max_exp</span></code></td>
<td>DBL_MAX_EXP</td>
<td>maximum integer e such that <code class="docutils literal"><span class="pre">radix**(e-1)</span></code> is
a representable finite float</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">max_10_exp</span></code></td>
<td>DBL_MAX_10_EXP</td>
<td>maximum integer e such that <code class="docutils literal"><span class="pre">10**e</span></code> is in the
range of representable finite floats</td>
</tr>
<tr class="row-even"><td><a class="reference internal" href="functions.html#min" title="min"><code class="xref py py-const docutils literal"><span class="pre">min</span></code></a></td>
<td>DBL_MIN</td>
<td>minimum positive normalized float</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">min_exp</span></code></td>
<td>DBL_MIN_EXP</td>
<td>minimum integer e such that <code class="docutils literal"><span class="pre">radix**(e-1)</span></code> is
a normalized float</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">min_10_exp</span></code></td>
<td>DBL_MIN_10_EXP</td>
<td>minimum integer e such that <code class="docutils literal"><span class="pre">10**e</span></code> is a
normalized float</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">radix</span></code></td>
<td>FLT_RADIX</td>
<td>radix of exponent representation</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">rounds</span></code></td>
<td>FLT_ROUNDS</td>
<td>integer constant representing the rounding mode
used for arithmetic operations. This reflects
the value of the system FLT_ROUNDS macro at
interpreter startup time. See section 5.2.4.2.2
of the C99 standard for an explanation of the
possible values and their meanings.</td>
</tr>
</tbody>
</table>
<p>The attribute <code class="xref py py-attr docutils literal"><span class="pre">sys.float_info.dig</span></code> needs further explanation. If
<code class="docutils literal"><span class="pre">s</span></code> is any string representing a decimal number with at most
<code class="xref py py-attr docutils literal"><span class="pre">sys.float_info.dig</span></code> significant digits, then converting <code class="docutils literal"><span class="pre">s</span></code> to a
float and back again will recover a string representing the same decimal
value:</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">sys</span>
<span class="gp">>>> </span><span class="n">sys</span><span class="o">.</span><span class="n">float_info</span><span class="o">.</span><span class="n">dig</span>
<span class="go">15</span>
<span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="s1">'3.14159265358979'</span> <span class="c1"># decimal string with 15 significant digits</span>
<span class="gp">>>> </span><span class="nb">format</span><span class="p">(</span><span class="nb">float</span><span class="p">(</span><span class="n">s</span><span class="p">),</span> <span class="s1">'.15g'</span><span class="p">)</span> <span class="c1"># convert to float and back -> same value</span>
<span class="go">'3.14159265358979'</span>
</pre></div>
</div>
<p>But for strings with more than <code class="xref py py-attr docutils literal"><span class="pre">sys.float_info.dig</span></code> significant digits,
this isn’t always true:</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="s1">'9876543211234567'</span> <span class="c1"># 16 significant digits is too many!</span>
<span class="gp">>>> </span><span class="nb">format</span><span class="p">(</span><span class="nb">float</span><span class="p">(</span><span class="n">s</span><span class="p">),</span> <span class="s1">'.16g'</span><span class="p">)</span> <span class="c1"># conversion changes value</span>
<span class="go">'9876543211234568'</span>
</pre></div>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.float_repr_style">
<code class="descclassname">sys.</code><code class="descname">float_repr_style</code><a class="headerlink" href="#sys.float_repr_style" title="Permalink to this definition">¶</a></dt>
<dd><p>A string indicating how the <a class="reference internal" href="functions.html#repr" title="repr"><code class="xref py py-func docutils literal"><span class="pre">repr()</span></code></a> function behaves for
floats. If the string has value <code class="docutils literal"><span class="pre">'short'</span></code> then for a finite
float <code class="docutils literal"><span class="pre">x</span></code>, <code class="docutils literal"><span class="pre">repr(x)</span></code> aims to produce a short string with the
property that <code class="docutils literal"><span class="pre">float(repr(x))</span> <span class="pre">==</span> <span class="pre">x</span></code>. This is the usual behaviour
in Python 3.1 and later. Otherwise, <code class="docutils literal"><span class="pre">float_repr_style</span></code> has value
<code class="docutils literal"><span class="pre">'legacy'</span></code> and <code class="docutils literal"><span class="pre">repr(x)</span></code> behaves in the same way as it did in
versions of Python prior to 3.1.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.1.</span></p>
</div>
</dd></dl>
<dl class="function">
<dt id="sys.getallocatedblocks">
<code class="descclassname">sys.</code><code class="descname">getallocatedblocks</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.getallocatedblocks" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the number of memory blocks currently allocated by the interpreter,
regardless of their size. This function is mainly useful for tracking
and debugging memory leaks. Because of the interpreter’s internal
caches, the result can vary from call to call; you may have to call
<a class="reference internal" href="#sys._clear_type_cache" title="sys._clear_type_cache"><code class="xref py py-func docutils literal"><span class="pre">_clear_type_cache()</span></code></a> and <a class="reference internal" href="gc.html#gc.collect" title="gc.collect"><code class="xref py py-func docutils literal"><span class="pre">gc.collect()</span></code></a> to get more
predictable results.</p>
<p>If a Python build or implementation cannot reasonably compute this
information, <a class="reference internal" href="#sys.getallocatedblocks" title="sys.getallocatedblocks"><code class="xref py py-func docutils literal"><span class="pre">getallocatedblocks()</span></code></a> is allowed to return 0 instead.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.4.</span></p>
</div>
</dd></dl>
<dl class="function">
<dt id="sys.getcheckinterval">
<code class="descclassname">sys.</code><code class="descname">getcheckinterval</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.getcheckinterval" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the interpreter’s “check interval”; see <a class="reference internal" href="#sys.setcheckinterval" title="sys.setcheckinterval"><code class="xref py py-func docutils literal"><span class="pre">setcheckinterval()</span></code></a>.</p>
<div class="deprecated">
<p><span class="versionmodified">Deprecated since version 3.2: </span>Use <a class="reference internal" href="#sys.getswitchinterval" title="sys.getswitchinterval"><code class="xref py py-func docutils literal"><span class="pre">getswitchinterval()</span></code></a> instead.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="sys.getdefaultencoding">
<code class="descclassname">sys.</code><code class="descname">getdefaultencoding</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.getdefaultencoding" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the name of the current default string encoding used by the Unicode
implementation.</p>
</dd></dl>
<dl class="function">
<dt id="sys.getdlopenflags">
<code class="descclassname">sys.</code><code class="descname">getdlopenflags</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.getdlopenflags" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current value of the flags that are used for
<code class="xref c c-func docutils literal"><span class="pre">dlopen()</span></code> calls. Symbolic names for the flag values can be
found in the <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal"><span class="pre">os</span></code></a> module (<code class="docutils literal"><span class="pre">RTLD_xxx</span></code> constants, e.g.
<a class="reference internal" href="os.html#os.RTLD_LAZY" title="os.RTLD_LAZY"><code class="xref py py-data docutils literal"><span class="pre">os.RTLD_LAZY</span></code></a>). Availability: Unix.</p>
</dd></dl>
<dl class="function">
<dt id="sys.getfilesystemencoding">
<code class="descclassname">sys.</code><code class="descname">getfilesystemencoding</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.getfilesystemencoding" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the name of the encoding used to convert Unicode filenames into
system file names. The result value depends on the operating system:</p>
<ul class="simple">
<li>On Mac OS X, the encoding is <code class="docutils literal"><span class="pre">'utf-8'</span></code>.</li>
<li>On Unix, the encoding is the user’s preference according to the result of
nl_langinfo(CODESET).</li>
<li>On Windows NT+, file names are Unicode natively, so no conversion is
performed. <a class="reference internal" href="#sys.getfilesystemencoding" title="sys.getfilesystemencoding"><code class="xref py py-func docutils literal"><span class="pre">getfilesystemencoding()</span></code></a> still returns <code class="docutils literal"><span class="pre">'mbcs'</span></code>, as
this is the encoding that applications should use when they explicitly
want to convert Unicode strings to byte strings that are equivalent when
used as file names.</li>
<li>On Windows 9x, the encoding is <code class="docutils literal"><span class="pre">'mbcs'</span></code>.</li>
</ul>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.2: </span><a class="reference internal" href="#sys.getfilesystemencoding" title="sys.getfilesystemencoding"><code class="xref py py-func docutils literal"><span class="pre">getfilesystemencoding()</span></code></a> result cannot be <code class="docutils literal"><span class="pre">None</span></code> anymore.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="sys.getrefcount">
<code class="descclassname">sys.</code><code class="descname">getrefcount</code><span class="sig-paren">(</span><em>object</em><span class="sig-paren">)</span><a class="headerlink" href="#sys.getrefcount" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the reference count of the <em>object</em>. The count returned is generally one
higher than you might expect, because it includes the (temporary) reference as
an argument to <a class="reference internal" href="#sys.getrefcount" title="sys.getrefcount"><code class="xref py py-func docutils literal"><span class="pre">getrefcount()</span></code></a>.</p>
</dd></dl>
<dl class="function">
<dt id="sys.getrecursionlimit">
<code class="descclassname">sys.</code><code class="descname">getrecursionlimit</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.getrecursionlimit" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current value of the recursion limit, the maximum depth of the Python
interpreter stack. This limit prevents infinite recursion from causing an
overflow of the C stack and crashing Python. It can be set by
<a class="reference internal" href="#sys.setrecursionlimit" title="sys.setrecursionlimit"><code class="xref py py-func docutils literal"><span class="pre">setrecursionlimit()</span></code></a>.</p>
</dd></dl>
<dl class="function">
<dt id="sys.getsizeof">
<code class="descclassname">sys.</code><code class="descname">getsizeof</code><span class="sig-paren">(</span><em>object</em><span class="optional">[</span>, <em>default</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.getsizeof" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the size of an object in bytes. The object can be any type of
object. All built-in objects will return correct results, but this
does not have to hold true for third-party extensions as it is implementation
specific.</p>
<p>Only the memory consumption directly attributed to the object is
accounted for, not the memory consumption of objects it refers to.</p>
<p>If given, <em>default</em> will be returned if the object does not provide means to
retrieve the size. Otherwise a <a class="reference internal" href="exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal"><span class="pre">TypeError</span></code></a> will be raised.</p>
<p><a class="reference internal" href="#sys.getsizeof" title="sys.getsizeof"><code class="xref py py-func docutils literal"><span class="pre">getsizeof()</span></code></a> calls the object’s <code class="docutils literal"><span class="pre">__sizeof__</span></code> method and adds an
additional garbage collector overhead if the object is managed by the garbage
collector.</p>
<p>See <a class="reference external" href="https://code.activestate.com/recipes/577504">recursive sizeof recipe</a>
for an example of using <a class="reference internal" href="#sys.getsizeof" title="sys.getsizeof"><code class="xref py py-func docutils literal"><span class="pre">getsizeof()</span></code></a> recursively to find the size of
containers and all their contents.</p>
</dd></dl>
<dl class="function">
<dt id="sys.getswitchinterval">
<code class="descclassname">sys.</code><code class="descname">getswitchinterval</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.getswitchinterval" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the interpreter’s “thread switch interval”; see
<a class="reference internal" href="#sys.setswitchinterval" title="sys.setswitchinterval"><code class="xref py py-func docutils literal"><span class="pre">setswitchinterval()</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.2.</span></p>
</div>
</dd></dl>
<dl class="function">
<dt id="sys._getframe">
<code class="descclassname">sys.</code><code class="descname">_getframe</code><span class="sig-paren">(</span><span class="optional">[</span><em>depth</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#sys._getframe" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a frame object from the call stack. If optional integer <em>depth</em> is
given, return the frame object that many calls below the top of the stack. If
that is deeper than the call stack, <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal"><span class="pre">ValueError</span></code></a> is raised. The default
for <em>depth</em> is zero, returning the frame at the top of the call stack.</p>
<div class="impl-detail compound">
<p><strong>CPython implementation detail:</strong> This function should be used for internal and specialized purposes only.
It is not guaranteed to exist in all implementations of Python.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="sys.getprofile">
<code class="descclassname">sys.</code><code class="descname">getprofile</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.getprofile" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-3">Get the profiler function as set by <a class="reference internal" href="#sys.setprofile" title="sys.setprofile"><code class="xref py py-func docutils literal"><span class="pre">setprofile()</span></code></a>.</p>
</dd></dl>
<dl class="function">
<dt id="sys.gettrace">
<code class="descclassname">sys.</code><code class="descname">gettrace</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.gettrace" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-4">Get the trace function as set by <a class="reference internal" href="#sys.settrace" title="sys.settrace"><code class="xref py py-func docutils literal"><span class="pre">settrace()</span></code></a>.</p>
<div class="impl-detail compound">
<p><strong>CPython implementation detail:</strong> The <a class="reference internal" href="#sys.gettrace" title="sys.gettrace"><code class="xref py py-func docutils literal"><span class="pre">gettrace()</span></code></a> function is intended only for implementing debuggers,
profilers, coverage tools and the like. Its behavior is part of the
implementation platform, rather than part of the language definition, and
thus may not be available in all Python implementations.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="sys.getwindowsversion">
<code class="descclassname">sys.</code><code class="descname">getwindowsversion</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.getwindowsversion" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a named tuple describing the Windows version
currently running. The named elements are <em>major</em>, <em>minor</em>,
<em>build</em>, <em>platform</em>, <em>service_pack</em>, <em>service_pack_minor</em>,
<em>service_pack_major</em>, <em>suite_mask</em>, and <em>product_type</em>.
<em>service_pack</em> contains a string while all other values are
integers. The components can also be accessed by name, so
<code class="docutils literal"><span class="pre">sys.getwindowsversion()[0]</span></code> is equivalent to
<code class="docutils literal"><span class="pre">sys.getwindowsversion().major</span></code>. For compatibility with prior
versions, only the first 5 elements are retrievable by indexing.</p>
<p><em>platform</em> may be one of the following values:</p>
<table border="1" class="docutils">
<colgroup>
<col width="62%" />
<col width="38%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Constant</th>
<th class="head">Platform</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">0</span> <span class="pre">(VER_PLATFORM_WIN32s)</span></code></td>
<td>Win32s on Windows 3.1</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">1</span> <span class="pre">(VER_PLATFORM_WIN32_WINDOWS)</span></code></td>
<td>Windows 95/98/ME</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">2</span> <span class="pre">(VER_PLATFORM_WIN32_NT)</span></code></td>
<td>Windows NT/2000/XP/x64</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">3</span> <span class="pre">(VER_PLATFORM_WIN32_CE)</span></code></td>
<td>Windows CE</td>
</tr>
</tbody>
</table>
<p><em>product_type</em> may be one of the following values:</p>
<table border="1" class="docutils">
<colgroup>
<col width="54%" />
<col width="46%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Constant</th>
<th class="head">Meaning</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">1</span> <span class="pre">(VER_NT_WORKSTATION)</span></code></td>
<td>The system is a workstation.</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">2</span> <span class="pre">(VER_NT_DOMAIN_CONTROLLER)</span></code></td>
<td>The system is a domain
controller.</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">3</span> <span class="pre">(VER_NT_SERVER)</span></code></td>
<td>The system is a server, but not
a domain controller.</td>
</tr>
</tbody>
</table>
<p>This function wraps the Win32 <code class="xref c c-func docutils literal"><span class="pre">GetVersionEx()</span></code> function; see the
Microsoft documentation on <code class="xref c c-func docutils literal"><span class="pre">OSVERSIONINFOEX()</span></code> for more information
about these fields.</p>
<p>Availability: Windows.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.2: </span>Changed to a named tuple and added <em>service_pack_minor</em>,
<em>service_pack_major</em>, <em>suite_mask</em>, and <em>product_type</em>.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="sys.get_coroutine_wrapper">
<code class="descclassname">sys.</code><code class="descname">get_coroutine_wrapper</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.get_coroutine_wrapper" title="Permalink to this definition">¶</a></dt>
<dd><p>Returns <code class="docutils literal"><span class="pre">None</span></code>, or a wrapper set by <a class="reference internal" href="#sys.set_coroutine_wrapper" title="sys.set_coroutine_wrapper"><code class="xref py py-func docutils literal"><span class="pre">set_coroutine_wrapper()</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.5: </span>See <span class="target" id="index-5"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0492"><strong>PEP 492</strong></a> for more details.</p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">This function has been added on a provisional basis (see <span class="target" id="index-6"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0411"><strong>PEP 411</strong></a>
for details.) Use it only for debugging purposes.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.hash_info">
<code class="descclassname">sys.</code><code class="descname">hash_info</code><a class="headerlink" href="#sys.hash_info" title="Permalink to this definition">¶</a></dt>
<dd><p>A <a class="reference internal" href="../glossary.html#term-struct-sequence"><span class="xref std std-term">struct sequence</span></a> giving parameters of the numeric hash
implementation. For more details about hashing of numeric types, see
<a class="reference internal" href="stdtypes.html#numeric-hash"><span>Hashing of numeric types</span></a>.</p>
<table border="1" class="docutils">
<colgroup>
<col width="30%" />
<col width="70%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">attribute</th>
<th class="head">explanation</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">width</span></code></td>
<td>width in bits used for hash values</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">modulus</span></code></td>
<td>prime modulus P used for numeric hash scheme</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">inf</span></code></td>
<td>hash value returned for a positive infinity</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">nan</span></code></td>
<td>hash value returned for a nan</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">imag</span></code></td>
<td>multiplier used for the imaginary part of a
complex number</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">algorithm</span></code></td>
<td>name of the algorithm for hashing of str, bytes,
and memoryview</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">hash_bits</span></code></td>
<td>internal output size of the hash algorithm</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">seed_bits</span></code></td>
<td>size of the seed key of the hash algorithm</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.2.</span></p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.4: </span>Added <em>algorithm</em>, <em>hash_bits</em> and <em>seed_bits</em></p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.hexversion">
<code class="descclassname">sys.</code><code class="descname">hexversion</code><a class="headerlink" href="#sys.hexversion" title="Permalink to this definition">¶</a></dt>
<dd><p>The version number encoded as a single integer. This is guaranteed to increase
with each version, including proper support for non-production releases. For
example, to test that the Python interpreter is at least version 1.5.2, use:</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="n">sys</span><span class="o">.</span><span class="n">hexversion</span> <span class="o">>=</span> <span class="mh">0x010502F0</span><span class="p">:</span>
<span class="c1"># use some advanced feature</span>
<span class="o">...</span>
<span class="k">else</span><span class="p">:</span>
<span class="c1"># use an alternative implementation or warn the user</span>
<span class="o">...</span>
</pre></div>
</div>
<p>This is called <code class="docutils literal"><span class="pre">hexversion</span></code> since it only really looks meaningful when viewed
as the result of passing it to the built-in <a class="reference internal" href="functions.html#hex" title="hex"><code class="xref py py-func docutils literal"><span class="pre">hex()</span></code></a> function. The
<a class="reference internal" href="../glossary.html#term-struct-sequence"><span class="xref std std-term">struct sequence</span></a> <a class="reference internal" href="#sys.version_info" title="sys.version_info"><code class="xref py py-data docutils literal"><span class="pre">sys.version_info</span></code></a> may be used for a more
human-friendly encoding of the same information.</p>
<p>More details of <code class="docutils literal"><span class="pre">hexversion</span></code> can be found at <a class="reference internal" href="../c-api/apiabiversion.html#apiabiversion"><span>API and ABI Versioning</span></a>.</p>
</dd></dl>
<dl class="data">
<dt id="sys.implementation">
<code class="descclassname">sys.</code><code class="descname">implementation</code><a class="headerlink" href="#sys.implementation" title="Permalink to this definition">¶</a></dt>
<dd><p>An object containing information about the implementation of the
currently running Python interpreter. The following attributes are
required to exist in all Python implementations.</p>
<p><em>name</em> is the implementation’s identifier, e.g. <code class="docutils literal"><span class="pre">'cpython'</span></code>. The actual
string is defined by the Python implementation, but it is guaranteed to be
lower case.</p>
<p><em>version</em> is a named tuple, in the same format as
<a class="reference internal" href="#sys.version_info" title="sys.version_info"><code class="xref py py-data docutils literal"><span class="pre">sys.version_info</span></code></a>. It represents the version of the Python
<em>implementation</em>. This has a distinct meaning from the specific
version of the Python <em>language</em> to which the currently running
interpreter conforms, which <code class="docutils literal"><span class="pre">sys.version_info</span></code> represents. For
example, for PyPy 1.8 <code class="docutils literal"><span class="pre">sys.implementation.version</span></code> might be
<code class="docutils literal"><span class="pre">sys.version_info(1,</span> <span class="pre">8,</span> <span class="pre">0,</span> <span class="pre">'final',</span> <span class="pre">0)</span></code>, whereas <code class="docutils literal"><span class="pre">sys.version_info</span></code>
would be <code class="docutils literal"><span class="pre">sys.version_info(2,</span> <span class="pre">7,</span> <span class="pre">2,</span> <span class="pre">'final',</span> <span class="pre">0)</span></code>. For CPython they
are the same value, since it is the reference implementation.</p>
<p><em>hexversion</em> is the implementation version in hexadecimal format, like
<a class="reference internal" href="#sys.hexversion" title="sys.hexversion"><code class="xref py py-data docutils literal"><span class="pre">sys.hexversion</span></code></a>.</p>
<p><em>cache_tag</em> is the tag used by the import machinery in the filenames of
cached modules. By convention, it would be a composite of the
implementation’s name and version, like <code class="docutils literal"><span class="pre">'cpython-33'</span></code>. However, a
Python implementation may use some other value if appropriate. If
<code class="docutils literal"><span class="pre">cache_tag</span></code> is set to <code class="docutils literal"><span class="pre">None</span></code>, it indicates that module caching should
be disabled.</p>
<p><a class="reference internal" href="#sys.implementation" title="sys.implementation"><code class="xref py py-data docutils literal"><span class="pre">sys.implementation</span></code></a> may contain additional attributes specific to
the Python implementation. These non-standard attributes must start with
an underscore, and are not described here. Regardless of its contents,
<a class="reference internal" href="#sys.implementation" title="sys.implementation"><code class="xref py py-data docutils literal"><span class="pre">sys.implementation</span></code></a> will not change during a run of the interpreter,
nor between implementation versions. (It may change between Python
language versions, however.) See <span class="target" id="index-7"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0421"><strong>PEP 421</strong></a> for more information.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.3.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.int_info">
<code class="descclassname">sys.</code><code class="descname">int_info</code><a class="headerlink" href="#sys.int_info" title="Permalink to this definition">¶</a></dt>
<dd><p>A <a class="reference internal" href="../glossary.html#term-struct-sequence"><span class="xref std std-term">struct sequence</span></a> that holds information about Python’s internal
representation of integers. The attributes are read only.</p>
<table border="1" class="docutils">
<colgroup>
<col width="35%" />
<col width="65%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Attribute</th>
<th class="head">Explanation</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">bits_per_digit</span></code></td>
<td>number of bits held in each digit. Python
integers are stored internally in base
<code class="docutils literal"><span class="pre">2**int_info.bits_per_digit</span></code></td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">sizeof_digit</span></code></td>
<td>size in bytes of the C type used to
represent a digit</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.1.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.__interactivehook__">
<code class="descclassname">sys.</code><code class="descname">__interactivehook__</code><a class="headerlink" href="#sys.__interactivehook__" title="Permalink to this definition">¶</a></dt>
<dd><p>When this attribute exists, its value is automatically called (with no
arguments) when the interpreter is launched in <a class="reference internal" href="../tutorial/interpreter.html#tut-interactive"><span>interactive mode</span></a>. This is done after the <span class="target" id="index-8"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONSTARTUP"><code class="xref std std-envvar docutils literal"><span class="pre">PYTHONSTARTUP</span></code></a> file is
read, so that you can set this hook there. The <a class="reference internal" href="site.html#module-site" title="site: Module responsible for site-specific configuration."><code class="xref py py-mod docutils literal"><span class="pre">site</span></code></a> module
<a class="reference internal" href="site.html#rlcompleter-config"><span>sets this</span></a>.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.4.</span></p>
</div>
</dd></dl>
<dl class="function">
<dt id="sys.intern">
<code class="descclassname">sys.</code><code class="descname">intern</code><span class="sig-paren">(</span><em>string</em><span class="sig-paren">)</span><a class="headerlink" href="#sys.intern" title="Permalink to this definition">¶</a></dt>
<dd><p>Enter <em>string</em> in the table of “interned” strings and return the interned string
– which is <em>string</em> itself or a copy. Interning strings is useful to gain a
little performance on dictionary lookup – if the keys in a dictionary are
interned, and the lookup key is interned, the key comparisons (after hashing)
can be done by a pointer compare instead of a string compare. Normally, the
names used in Python programs are automatically interned, and the dictionaries
used to hold module, class or instance attributes have interned keys.</p>
<p>Interned strings are not immortal; you must keep a reference to the return
value of <a class="reference internal" href="#sys.intern" title="sys.intern"><code class="xref py py-func docutils literal"><span class="pre">intern()</span></code></a> around to benefit from it.</p>
</dd></dl>
<dl class="function">
<dt id="sys.is_finalizing">
<code class="descclassname">sys.</code><code class="descname">is_finalizing</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sys.is_finalizing" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal"><span class="pre">True</span></code></a> if the Python interpreter is
<a class="reference internal" href="../glossary.html#term-interpreter-shutdown"><span class="xref std std-term">shutting down</span></a>, <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal"><span class="pre">False</span></code></a> otherwise.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.5.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.last_type">
<code class="descclassname">sys.</code><code class="descname">last_type</code><a class="headerlink" href="#sys.last_type" title="Permalink to this definition">¶</a></dt>
<dt id="sys.last_value">
<code class="descclassname">sys.</code><code class="descname">last_value</code><a class="headerlink" href="#sys.last_value" title="Permalink to this definition">¶</a></dt>
<dt id="sys.last_traceback">
<code class="descclassname">sys.</code><code class="descname">last_traceback</code><a class="headerlink" href="#sys.last_traceback" title="Permalink to this definition">¶</a></dt>
<dd><p>These three variables are not always defined; they are set when an exception is
not handled and the interpreter prints an error message and a stack traceback.
Their intended use is to allow an interactive user to import a debugger module
and engage in post-mortem debugging without having to re-execute the command
that caused the error. (Typical use is <code class="docutils literal"><span class="pre">import</span> <span class="pre">pdb;</span> <span class="pre">pdb.pm()</span></code> to enter the
post-mortem debugger; see <a class="reference internal" href="pdb.html#module-pdb" title="pdb: The Python debugger for interactive interpreters."><code class="xref py py-mod docutils literal"><span class="pre">pdb</span></code></a> module for
more information.)</p>
<p>The meaning of the variables is the same as that of the return values from
<a class="reference internal" href="#sys.exc_info" title="sys.exc_info"><code class="xref py py-func docutils literal"><span class="pre">exc_info()</span></code></a> above.</p>
</dd></dl>
<dl class="data">
<dt id="sys.maxsize">
<code class="descclassname">sys.</code><code class="descname">maxsize</code><a class="headerlink" href="#sys.maxsize" title="Permalink to this definition">¶</a></dt>
<dd><p>An integer giving the maximum value a variable of type <code class="xref c c-type docutils literal"><span class="pre">Py_ssize_t</span></code> can
take. It’s usually <code class="docutils literal"><span class="pre">2**31</span> <span class="pre">-</span> <span class="pre">1</span></code> on a 32-bit platform and <code class="docutils literal"><span class="pre">2**63</span> <span class="pre">-</span> <span class="pre">1</span></code> on a
64-bit platform.</p>
</dd></dl>
<dl class="data">
<dt id="sys.maxunicode">
<code class="descclassname">sys.</code><code class="descname">maxunicode</code><a class="headerlink" href="#sys.maxunicode" title="Permalink to this definition">¶</a></dt>
<dd><p>An integer giving the value of the largest Unicode code point,
i.e. <code class="docutils literal"><span class="pre">1114111</span></code> (<code class="docutils literal"><span class="pre">0x10FFFF</span></code> in hexadecimal).</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3: </span>Before <span class="target" id="index-9"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0393"><strong>PEP 393</strong></a>, <code class="docutils literal"><span class="pre">sys.maxunicode</span></code> used to be either <code class="docutils literal"><span class="pre">0xFFFF</span></code>
or <code class="docutils literal"><span class="pre">0x10FFFF</span></code>, depending on the configuration option that specified
whether Unicode characters were stored as UCS-2 or UCS-4.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.meta_path">
<code class="descclassname">sys.</code><code class="descname">meta_path</code><a class="headerlink" href="#sys.meta_path" title="Permalink to this definition">¶</a></dt>
<dd><p>A list of <a class="reference internal" href="../glossary.html#term-meta-path-finder"><span class="xref std std-term">meta path finder</span></a> objects that have their
<a class="reference internal" href="importlib.html#importlib.abc.MetaPathFinder.find_spec" title="importlib.abc.MetaPathFinder.find_spec"><code class="xref py py-meth docutils literal"><span class="pre">find_spec()</span></code></a> methods called to see if one
of the objects can find the module to be imported. The
<a class="reference internal" href="importlib.html#importlib.abc.MetaPathFinder.find_spec" title="importlib.abc.MetaPathFinder.find_spec"><code class="xref py py-meth docutils literal"><span class="pre">find_spec()</span></code></a> method is called with at
least the absolute name of the module being imported. If the module to be
imported is contained in a package, then the parent package’s <a class="reference internal" href="../reference/import.html#__path__" title="__path__"><code class="xref py py-attr docutils literal"><span class="pre">__path__</span></code></a>
attribute is passed in as a second argument. The method returns a
<a class="reference internal" href="../glossary.html#term-module-spec"><span class="xref std std-term">module spec</span></a>, or <code class="docutils literal"><span class="pre">None</span></code> if the module cannot be found.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><a class="reference internal" href="importlib.html#importlib.abc.MetaPathFinder" title="importlib.abc.MetaPathFinder"><code class="xref py py-class docutils literal"><span class="pre">importlib.abc.MetaPathFinder</span></code></a></dt>
<dd>The abstract base class defining the interface of finder objects on
<a class="reference internal" href="#sys.meta_path" title="sys.meta_path"><code class="xref py py-data docutils literal"><span class="pre">meta_path</span></code></a>.</dd>
<dt><a class="reference internal" href="importlib.html#importlib.machinery.ModuleSpec" title="importlib.machinery.ModuleSpec"><code class="xref py py-class docutils literal"><span class="pre">importlib.machinery.ModuleSpec</span></code></a></dt>
<dd>The concrete class which
<a class="reference internal" href="importlib.html#importlib.abc.MetaPathFinder.find_spec" title="importlib.abc.MetaPathFinder.find_spec"><code class="xref py py-meth docutils literal"><span class="pre">find_spec()</span></code></a> should return
instances of.</dd>
</dl>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.4: </span><a class="reference internal" href="../glossary.html#term-module-spec"><span class="xref std std-term">Module specs</span></a> were introduced in Python 3.4, by
<span class="target" id="index-10"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0451"><strong>PEP 451</strong></a>. Earlier versions of Python looked for a method called
<a class="reference internal" href="importlib.html#importlib.abc.MetaPathFinder.find_module" title="importlib.abc.MetaPathFinder.find_module"><code class="xref py py-meth docutils literal"><span class="pre">find_module()</span></code></a>.
This is still called as a fallback if a <a class="reference internal" href="#sys.meta_path" title="sys.meta_path"><code class="xref py py-data docutils literal"><span class="pre">meta_path</span></code></a> entry doesn’t
have a <a class="reference internal" href="importlib.html#importlib.abc.MetaPathFinder.find_spec" title="importlib.abc.MetaPathFinder.find_spec"><code class="xref py py-meth docutils literal"><span class="pre">find_spec()</span></code></a> method.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.modules">
<code class="descclassname">sys.</code><code class="descname">modules</code><a class="headerlink" href="#sys.modules" title="Permalink to this definition">¶</a></dt>
<dd><p>This is a dictionary that maps module names to modules which have already been
loaded. This can be manipulated to force reloading of modules and other tricks.
However, replacing the dictionary will not necessarily work as expected and
deleting essential items from the dictionary may cause Python to fail.</p>
</dd></dl>
<dl class="data">
<dt id="sys.path">
<code class="descclassname">sys.</code><code class="descname">path</code><a class="headerlink" href="#sys.path" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-11">A list of strings that specifies the search path for modules. Initialized from
the environment variable <span class="target" id="index-12"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONPATH"><code class="xref std std-envvar docutils literal"><span class="pre">PYTHONPATH</span></code></a>, plus an installation-dependent
default.</p>
<p>As initialized upon program startup, the first item of this list, <code class="docutils literal"><span class="pre">path[0]</span></code>,
is the directory containing the script that was used to invoke the Python
interpreter. If the script directory is not available (e.g. if the interpreter
is invoked interactively or if the script is read from standard input),
<code class="docutils literal"><span class="pre">path[0]</span></code> is the empty string, which directs Python to search modules in the
current directory first. Notice that the script directory is inserted <em>before</em>
the entries inserted as a result of <span class="target" id="index-13"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONPATH"><code class="xref std std-envvar docutils literal"><span class="pre">PYTHONPATH</span></code></a>.</p>
<p>A program is free to modify this list for its own purposes. Only strings
and bytes should be added to <a class="reference internal" href="#sys.path" title="sys.path"><code class="xref py py-data docutils literal"><span class="pre">sys.path</span></code></a>; all other data types are
ignored during import.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">Module <a class="reference internal" href="site.html#module-site" title="site: Module responsible for site-specific configuration."><code class="xref py py-mod docutils literal"><span class="pre">site</span></code></a> This describes how to use .pth files to extend
<a class="reference internal" href="#sys.path" title="sys.path"><code class="xref py py-data docutils literal"><span class="pre">sys.path</span></code></a>.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.path_hooks">
<code class="descclassname">sys.</code><code class="descname">path_hooks</code><a class="headerlink" href="#sys.path_hooks" title="Permalink to this definition">¶</a></dt>
<dd><p>A list of callables that take a path argument to try to create a
<a class="reference internal" href="../glossary.html#term-finder"><span class="xref std std-term">finder</span></a> for the path. If a finder can be created, it is to be
returned by the callable, else raise <a class="reference internal" href="exceptions.html#ImportError" title="ImportError"><code class="xref py py-exc docutils literal"><span class="pre">ImportError</span></code></a>.</p>
<p>Originally specified in <span class="target" id="index-14"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a>.</p>
</dd></dl>
<dl class="data">
<dt id="sys.path_importer_cache">
<code class="descclassname">sys.</code><code class="descname">path_importer_cache</code><a class="headerlink" href="#sys.path_importer_cache" title="Permalink to this definition">¶</a></dt>
<dd><p>A dictionary acting as a cache for <a class="reference internal" href="../glossary.html#term-finder"><span class="xref std std-term">finder</span></a> objects. The keys are
paths that have been passed to <a class="reference internal" href="#sys.path_hooks" title="sys.path_hooks"><code class="xref py py-data docutils literal"><span class="pre">sys.path_hooks</span></code></a> and the values are
the finders that are found. If a path is a valid file system path but no
finder is found on <a class="reference internal" href="#sys.path_hooks" title="sys.path_hooks"><code class="xref py py-data docutils literal"><span class="pre">sys.path_hooks</span></code></a> then <code class="docutils literal"><span class="pre">None</span></code> is
stored.</p>
<p>Originally specified in <span class="target" id="index-15"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a>.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3: </span><code class="docutils literal"><span class="pre">None</span></code> is stored instead of <a class="reference internal" href="imp.html#imp.NullImporter" title="imp.NullImporter"><code class="xref py py-class docutils literal"><span class="pre">imp.NullImporter</span></code></a> when no finder
is found.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.platform">
<code class="descclassname">sys.</code><code class="descname">platform</code><a class="headerlink" href="#sys.platform" title="Permalink to this definition">¶</a></dt>
<dd><p>This string contains a platform identifier that can be used to append
platform-specific components to <a class="reference internal" href="#sys.path" title="sys.path"><code class="xref py py-data docutils literal"><span class="pre">sys.path</span></code></a>, for instance.</p>
<p>For Unix systems, except on Linux, this is the lowercased OS name as
returned by <code class="docutils literal"><span class="pre">uname</span> <span class="pre">-s</span></code> with the first part of the version as returned by
<code class="docutils literal"><span class="pre">uname</span> <span class="pre">-r</span></code> appended, e.g. <code class="docutils literal"><span class="pre">'sunos5'</span></code> or <code class="docutils literal"><span class="pre">'freebsd8'</span></code>, <em>at the time
when Python was built</em>. Unless you want to test for a specific system
version, it is therefore recommended to use the following idiom:</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="n">sys</span><span class="o">.</span><span class="n">platform</span><span class="o">.</span><span class="n">startswith</span><span class="p">(</span><span class="s1">'freebsd'</span><span class="p">):</span>
<span class="c1"># FreeBSD-specific code here...</span>
<span class="k">elif</span> <span class="n">sys</span><span class="o">.</span><span class="n">platform</span><span class="o">.</span><span class="n">startswith</span><span class="p">(</span><span class="s1">'linux'</span><span class="p">):</span>
<span class="c1"># Linux-specific code here...</span>
</pre></div>
</div>
<p>For other systems, the values are:</p>
<table border="1" class="docutils">
<colgroup>
<col width="37%" />
<col width="63%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">System</th>
<th class="head"><code class="docutils literal"><span class="pre">platform</span></code> value</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>Linux</td>
<td><code class="docutils literal"><span class="pre">'linux'</span></code></td>
</tr>
<tr class="row-odd"><td>Windows</td>
<td><code class="docutils literal"><span class="pre">'win32'</span></code></td>
</tr>
<tr class="row-even"><td>Windows/Cygwin</td>
<td><code class="docutils literal"><span class="pre">'cygwin'</span></code></td>
</tr>
<tr class="row-odd"><td>Mac OS X</td>
<td><code class="docutils literal"><span class="pre">'darwin'</span></code></td>
</tr>
</tbody>
</table>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3: </span>On Linux, <a class="reference internal" href="#sys.platform" title="sys.platform"><code class="xref py py-attr docutils literal"><span class="pre">sys.platform</span></code></a> doesn’t contain the major version anymore.
It is always <code class="docutils literal"><span class="pre">'linux'</span></code>, instead of <code class="docutils literal"><span class="pre">'linux2'</span></code> or <code class="docutils literal"><span class="pre">'linux3'</span></code>. Since
older Python versions include the version number, it is recommended to
always use the <code class="docutils literal"><span class="pre">startswith</span></code> idiom presented above.</p>
</div>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p><a class="reference internal" href="os.html#os.name" title="os.name"><code class="xref py py-attr docutils literal"><span class="pre">os.name</span></code></a> has a coarser granularity. <a class="reference internal" href="os.html#os.uname" title="os.uname"><code class="xref py py-func docutils literal"><span class="pre">os.uname()</span></code></a> gives
system-dependent version information.</p>
<p class="last">The <a class="reference internal" href="platform.html#module-platform" title="platform: Retrieves as much platform identifying data as possible."><code class="xref py py-mod docutils literal"><span class="pre">platform</span></code></a> module provides detailed checks for the
system’s identity.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.prefix">
<code class="descclassname">sys.</code><code class="descname">prefix</code><a class="headerlink" href="#sys.prefix" title="Permalink to this definition">¶</a></dt>
<dd><p>A string giving the site-specific directory prefix where the platform
independent Python files are installed; by default, this is the string
<code class="docutils literal"><span class="pre">'/usr/local'</span></code>. This can be set at build time with the <code class="docutils literal"><span class="pre">--prefix</span></code>
argument to the <strong class="program">configure</strong> script. The main collection of Python
library modules is installed in the directory <code class="file docutils literal"><em><span class="pre">prefix</span></em><span class="pre">/lib/python</span><em><span class="pre">X.Y</span></em></code>
while the platform independent header files (all except <code class="file docutils literal"><span class="pre">pyconfig.h</span></code>) are
stored in <code class="file docutils literal"><em><span class="pre">prefix</span></em><span class="pre">/include/python</span><em><span class="pre">X.Y</span></em></code>, where <em>X.Y</em> is the version
number of Python, for example <code class="docutils literal"><span class="pre">3.2</span></code>.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">If a <a class="reference internal" href="venv.html#venv-def"><span>virtual environment</span></a> is in effect, this
value will be changed in <code class="docutils literal"><span class="pre">site.py</span></code> to point to the virtual
environment. The value for the Python installation will still be
available, via <a class="reference internal" href="#sys.base_prefix" title="sys.base_prefix"><code class="xref py py-data docutils literal"><span class="pre">base_prefix</span></code></a>.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.ps1">
<code class="descclassname">sys.</code><code class="descname">ps1</code><a class="headerlink" href="#sys.ps1" title="Permalink to this definition">¶</a></dt>
<dt id="sys.ps2">
<code class="descclassname">sys.</code><code class="descname">ps2</code><a class="headerlink" href="#sys.ps2" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-16">Strings specifying the primary and secondary prompt of the interpreter. These
are only defined if the interpreter is in interactive mode. Their initial
values in this case are <code class="docutils literal"><span class="pre">'>>></span> <span class="pre">'</span></code> and <code class="docutils literal"><span class="pre">'...</span> <span class="pre">'</span></code>. If a non-string object is
assigned to either variable, its <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-func docutils literal"><span class="pre">str()</span></code></a> is re-evaluated each time the
interpreter prepares to read a new interactive command; this can be used to
implement a dynamic prompt.</p>
</dd></dl>
<dl class="function">
<dt id="sys.setcheckinterval">
<code class="descclassname">sys.</code><code class="descname">setcheckinterval</code><span class="sig-paren">(</span><em>interval</em><span class="sig-paren">)</span><a class="headerlink" href="#sys.setcheckinterval" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the interpreter’s “check interval”. This integer value determines how often
the interpreter checks for periodic things such as thread switches and signal
handlers. The default is <code class="docutils literal"><span class="pre">100</span></code>, meaning the check is performed every 100
Python virtual instructions. Setting it to a larger value may increase
performance for programs using threads. Setting it to a value <code class="docutils literal"><span class="pre"><=</span></code> 0 checks
every virtual instruction, maximizing responsiveness as well as overhead.</p>
<div class="deprecated">
<p><span class="versionmodified">Deprecated since version 3.2: </span>This function doesn’t have an effect anymore, as the internal logic for
thread switching and asynchronous tasks has been rewritten. Use
<a class="reference internal" href="#sys.setswitchinterval" title="sys.setswitchinterval"><code class="xref py py-func docutils literal"><span class="pre">setswitchinterval()</span></code></a> instead.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="sys.setdlopenflags">
<code class="descclassname">sys.</code><code class="descname">setdlopenflags</code><span class="sig-paren">(</span><em>n</em><span class="sig-paren">)</span><a class="headerlink" href="#sys.setdlopenflags" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the flags used by the interpreter for <code class="xref c c-func docutils literal"><span class="pre">dlopen()</span></code> calls, such as when
the interpreter loads extension modules. Among other things, this will enable a
lazy resolving of symbols when importing a module, if called as
<code class="docutils literal"><span class="pre">sys.setdlopenflags(0)</span></code>. To share symbols across extension modules, call as
<code class="docutils literal"><span class="pre">sys.setdlopenflags(os.RTLD_GLOBAL)</span></code>. Symbolic names for the flag values
can be found in the <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal"><span class="pre">os</span></code></a> module (<code class="docutils literal"><span class="pre">RTLD_xxx</span></code> constants, e.g.
<a class="reference internal" href="os.html#os.RTLD_LAZY" title="os.RTLD_LAZY"><code class="xref py py-data docutils literal"><span class="pre">os.RTLD_LAZY</span></code></a>).</p>
<p>Availability: Unix.</p>
</dd></dl>
<dl class="function">
<dt id="sys.setprofile">
<code class="descclassname">sys.</code><code class="descname">setprofile</code><span class="sig-paren">(</span><em>profilefunc</em><span class="sig-paren">)</span><a class="headerlink" href="#sys.setprofile" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-17">Set the system’s profile function, which allows you to implement a Python source
code profiler in Python. See chapter <a class="reference internal" href="profile.html#profile"><span>The Python Profilers</span></a> for more information on the
Python profiler. The system’s profile function is called similarly to the
system’s trace function (see <a class="reference internal" href="#sys.settrace" title="sys.settrace"><code class="xref py py-func docutils literal"><span class="pre">settrace()</span></code></a>), but it isn’t called for each
executed line of code (only on call and return, but the return event is reported
even when an exception has been set). The function is thread-specific, but
there is no way for the profiler to know about context switches between threads,
so it does not make sense to use this in the presence of multiple threads. Also,
its return value is not used, so it can simply return <code class="docutils literal"><span class="pre">None</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="sys.setrecursionlimit">
<code class="descclassname">sys.</code><code class="descname">setrecursionlimit</code><span class="sig-paren">(</span><em>limit</em><span class="sig-paren">)</span><a class="headerlink" href="#sys.setrecursionlimit" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the maximum depth of the Python interpreter stack to <em>limit</em>. This limit
prevents infinite recursion from causing an overflow of the C stack and crashing
Python.</p>
<p>The highest possible limit is platform-dependent. A user may need to set the
limit higher when they have a program that requires deep recursion and a platform
that supports a higher limit. This should be done with care, because a too-high
limit can lead to a crash.</p>
<p>If the new limit is too low at the current recursion depth, a
<a class="reference internal" href="exceptions.html#RecursionError" title="RecursionError"><code class="xref py py-exc docutils literal"><span class="pre">RecursionError</span></code></a> exception is raised.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.5.1: </span>A <a class="reference internal" href="exceptions.html#RecursionError" title="RecursionError"><code class="xref py py-exc docutils literal"><span class="pre">RecursionError</span></code></a> exception is now raised if the new limit is too
low at the current recursion depth.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="sys.setswitchinterval">
<code class="descclassname">sys.</code><code class="descname">setswitchinterval</code><span class="sig-paren">(</span><em>interval</em><span class="sig-paren">)</span><a class="headerlink" href="#sys.setswitchinterval" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the interpreter’s thread switch interval (in seconds). This floating-point
value determines the ideal duration of the “timeslices” allocated to
concurrently running Python threads. Please note that the actual value
can be higher, especially if long-running internal functions or methods
are used. Also, which thread becomes scheduled at the end of the interval
is the operating system’s decision. The interpreter doesn’t have its
own scheduler.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.2.</span></p>
</div>
</dd></dl>
<dl class="function">
<dt id="sys.settrace">
<code class="descclassname">sys.</code><code class="descname">settrace</code><span class="sig-paren">(</span><em>tracefunc</em><span class="sig-paren">)</span><a class="headerlink" href="#sys.settrace" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-18">Set the system’s trace function, which allows you to implement a Python
source code debugger in Python. The function is thread-specific; for a
debugger to support multiple threads, it must be registered using
<a class="reference internal" href="#sys.settrace" title="sys.settrace"><code class="xref py py-func docutils literal"><span class="pre">settrace()</span></code></a> for each thread being debugged.</p>
<p>Trace functions should have three arguments: <em>frame</em>, <em>event</em>, and
<em>arg</em>. <em>frame</em> is the current stack frame. <em>event</em> is a string: <code class="docutils literal"><span class="pre">'call'</span></code>,
<code class="docutils literal"><span class="pre">'line'</span></code>, <code class="docutils literal"><span class="pre">'return'</span></code>, <code class="docutils literal"><span class="pre">'exception'</span></code>, <code class="docutils literal"><span class="pre">'c_call'</span></code>, <code class="docutils literal"><span class="pre">'c_return'</span></code>, or
<code class="docutils literal"><span class="pre">'c_exception'</span></code>. <em>arg</em> depends on the event type.</p>
<p>The trace function is invoked (with <em>event</em> set to <code class="docutils literal"><span class="pre">'call'</span></code>) whenever a new
local scope is entered; it should return a reference to a local trace
function to be used that scope, or <code class="docutils literal"><span class="pre">None</span></code> if the scope shouldn’t be traced.</p>
<p>The local trace function should return a reference to itself (or to another
function for further tracing in that scope), or <code class="docutils literal"><span class="pre">None</span></code> to turn off tracing
in that scope.</p>
<p>The events have the following meaning:</p>
<dl class="docutils">
<dt><code class="docutils literal"><span class="pre">'call'</span></code></dt>
<dd>A function is called (or some other code block entered). The
global trace function is called; <em>arg</em> is <code class="docutils literal"><span class="pre">None</span></code>; the return value
specifies the local trace function.</dd>
<dt><code class="docutils literal"><span class="pre">'line'</span></code></dt>
<dd>The interpreter is about to execute a new line of code or re-execute the
condition of a loop. The local trace function is called; <em>arg</em> is
<code class="docutils literal"><span class="pre">None</span></code>; the return value specifies the new local trace function. See
<code class="file docutils literal"><span class="pre">Objects/lnotab_notes.txt</span></code> for a detailed explanation of how this
works.</dd>
<dt><code class="docutils literal"><span class="pre">'return'</span></code></dt>
<dd>A function (or other code block) is about to return. The local trace
function is called; <em>arg</em> is the value that will be returned, or <code class="docutils literal"><span class="pre">None</span></code>
if the event is caused by an exception being raised. The trace function’s
return value is ignored.</dd>
<dt><code class="docutils literal"><span class="pre">'exception'</span></code></dt>
<dd>An exception has occurred. The local trace function is called; <em>arg</em> is a
tuple <code class="docutils literal"><span class="pre">(exception,</span> <span class="pre">value,</span> <span class="pre">traceback)</span></code>; the return value specifies the
new local trace function.</dd>
<dt><code class="docutils literal"><span class="pre">'c_call'</span></code></dt>
<dd>A C function is about to be called. This may be an extension function or
a built-in. <em>arg</em> is the C function object.</dd>
<dt><code class="docutils literal"><span class="pre">'c_return'</span></code></dt>
<dd>A C function has returned. <em>arg</em> is the C function object.</dd>
<dt><code class="docutils literal"><span class="pre">'c_exception'</span></code></dt>
<dd>A C function has raised an exception. <em>arg</em> is the C function object.</dd>
</dl>
<p>Note that as an exception is propagated down the chain of callers, an
<code class="docutils literal"><span class="pre">'exception'</span></code> event is generated at each level.</p>
<p>For more information on code and frame objects, refer to <a class="reference internal" href="../reference/datamodel.html#types"><span>The standard type hierarchy</span></a>.</p>
<div class="impl-detail compound">
<p><strong>CPython implementation detail:</strong> The <a class="reference internal" href="#sys.settrace" title="sys.settrace"><code class="xref py py-func docutils literal"><span class="pre">settrace()</span></code></a> function is intended only for implementing debuggers,
profilers, coverage tools and the like. Its behavior is part of the
implementation platform, rather than part of the language definition, and
thus may not be available in all Python implementations.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="sys.settscdump">
<code class="descclassname">sys.</code><code class="descname">settscdump</code><span class="sig-paren">(</span><em>on_flag</em><span class="sig-paren">)</span><a class="headerlink" href="#sys.settscdump" title="Permalink to this definition">¶</a></dt>
<dd><p>Activate dumping of VM measurements using the Pentium timestamp counter, if
<em>on_flag</em> is true. Deactivate these dumps if <em>on_flag</em> is off. The function is
available only if Python was compiled with <code class="docutils literal"><span class="pre">--with-tsc</span></code>. To understand
the output of this dump, read <code class="file docutils literal"><span class="pre">Python/ceval.c</span></code> in the Python sources.</p>
<div class="impl-detail compound">
<p><strong>CPython implementation detail:</strong> This function is intimately bound to CPython implementation details and
thus not likely to be implemented elsewhere.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="sys.set_coroutine_wrapper">
<code class="descclassname">sys.</code><code class="descname">set_coroutine_wrapper</code><span class="sig-paren">(</span><em>wrapper</em><span class="sig-paren">)</span><a class="headerlink" href="#sys.set_coroutine_wrapper" title="Permalink to this definition">¶</a></dt>
<dd><p>Allows intercepting creation of <a class="reference internal" href="../glossary.html#term-coroutine"><span class="xref std std-term">coroutine</span></a> objects (only ones that
are created by an <a class="reference internal" href="../reference/compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal"><span class="pre">async</span> <span class="pre">def</span></code></a> function; generators decorated with
<a class="reference internal" href="types.html#types.coroutine" title="types.coroutine"><code class="xref py py-func docutils literal"><span class="pre">types.coroutine()</span></code></a> or <a class="reference internal" href="asyncio-task.html#asyncio.coroutine" title="asyncio.coroutine"><code class="xref py py-func docutils literal"><span class="pre">asyncio.coroutine()</span></code></a> will not be
intercepted).</p>
<p>The <em>wrapper</em> argument must be either:</p>
<ul class="simple">
<li>a callable that accepts one argument (a coroutine object);</li>
<li><code class="docutils literal"><span class="pre">None</span></code>, to reset the wrapper.</li>
</ul>
<p>If called twice, the new wrapper replaces the previous one. The function
is thread-specific.</p>
<p>The <em>wrapper</em> callable cannot define new coroutines directly or indirectly:</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">wrapper</span><span class="p">(</span><span class="n">coro</span><span class="p">):</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">wrap</span><span class="p">(</span><span class="n">coro</span><span class="p">):</span>
<span class="k">return</span> <span class="k">await</span> <span class="n">coro</span>
<span class="k">return</span> <span class="n">wrap</span><span class="p">(</span><span class="n">coro</span><span class="p">)</span>
<span class="n">sys</span><span class="o">.</span><span class="n">set_coroutine_wrapper</span><span class="p">(</span><span class="n">wrapper</span><span class="p">)</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">foo</span><span class="p">():</span>
<span class="k">pass</span>
<span class="c1"># The following line will fail with a RuntimeError, because</span>
<span class="c1"># ``wrapper`` creates a ``wrap(coro)`` coroutine:</span>
<span class="n">foo</span><span class="p">()</span>
</pre></div>
</div>
<p>See also <a class="reference internal" href="#sys.get_coroutine_wrapper" title="sys.get_coroutine_wrapper"><code class="xref py py-func docutils literal"><span class="pre">get_coroutine_wrapper()</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.5: </span>See <span class="target" id="index-19"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0492"><strong>PEP 492</strong></a> for more details.</p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">This function has been added on a provisional basis (see <span class="target" id="index-20"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0411"><strong>PEP 411</strong></a>
for details.) Use it only for debugging purposes.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.stdin">
<code class="descclassname">sys.</code><code class="descname">stdin</code><a class="headerlink" href="#sys.stdin" title="Permalink to this definition">¶</a></dt>
<dt id="sys.stdout">
<code class="descclassname">sys.</code><code class="descname">stdout</code><a class="headerlink" href="#sys.stdout" title="Permalink to this definition">¶</a></dt>
<dt id="sys.stderr">
<code class="descclassname">sys.</code><code class="descname">stderr</code><a class="headerlink" href="#sys.stderr" title="Permalink to this definition">¶</a></dt>
<dd><p><a class="reference internal" href="../glossary.html#term-file-object"><span class="xref std std-term">File objects</span></a> used by the interpreter for standard
input, output and errors:</p>
<ul class="simple">
<li><code class="docutils literal"><span class="pre">stdin</span></code> is used for all interactive input (including calls to
<a class="reference internal" href="functions.html#input" title="input"><code class="xref py py-func docutils literal"><span class="pre">input()</span></code></a>);</li>
<li><code class="docutils literal"><span class="pre">stdout</span></code> is used for the output of <a class="reference internal" href="functions.html#print" title="print"><code class="xref py py-func docutils literal"><span class="pre">print()</span></code></a> and <a class="reference internal" href="../glossary.html#term-expression"><span class="xref std std-term">expression</span></a>
statements and for the prompts of <a class="reference internal" href="functions.html#input" title="input"><code class="xref py py-func docutils literal"><span class="pre">input()</span></code></a>;</li>
<li>The interpreter’s own prompts and its error messages go to <code class="docutils literal"><span class="pre">stderr</span></code>.</li>
</ul>
<p>These streams are regular <a class="reference internal" href="../glossary.html#term-text-file"><span class="xref std std-term">text files</span></a> like those
returned by the <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal"><span class="pre">open()</span></code></a> function. Their parameters are chosen as
follows:</p>
<ul>
<li><p class="first">The character encoding is platform-dependent. Under Windows, if the stream
is interactive (that is, if its <code class="xref py py-meth docutils literal"><span class="pre">isatty()</span></code> method returns <code class="docutils literal"><span class="pre">True</span></code>), the
console codepage is used, otherwise the ANSI code page. Under other
platforms, the locale encoding is used (see <a class="reference internal" href="locale.html#locale.getpreferredencoding" title="locale.getpreferredencoding"><code class="xref py py-meth docutils literal"><span class="pre">locale.getpreferredencoding()</span></code></a>).</p>
<p>Under all platforms though, you can override this value by setting the
<span class="target" id="index-21"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONIOENCODING"><code class="xref std std-envvar docutils literal"><span class="pre">PYTHONIOENCODING</span></code></a> environment variable before starting Python.</p>
</li>
<li><p class="first">When interactive, standard streams are line-buffered. Otherwise, they
are block-buffered like regular text files. You can override this
value with the <a class="reference internal" href="../using/cmdline.html#cmdoption-u"><code class="xref std std-option docutils literal"><span class="pre">-u</span></code></a> command-line option.</p>
</li>
</ul>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p>To write or read binary data from/to the standard streams, use the
underlying binary <a class="reference internal" href="io.html#io.TextIOBase.buffer" title="io.TextIOBase.buffer"><code class="xref py py-data docutils literal"><span class="pre">buffer</span></code></a> object. For example, to
write bytes to <a class="reference internal" href="#sys.stdout" title="sys.stdout"><code class="xref py py-data docutils literal"><span class="pre">stdout</span></code></a>, use <code class="docutils literal"><span class="pre">sys.stdout.buffer.write(b'abc')</span></code>.</p>
<p class="last">However, if you are writing a library (and do not control in which
context its code will be executed), be aware that the standard streams
may be replaced with file-like objects like <a class="reference internal" href="io.html#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal"><span class="pre">io.StringIO</span></code></a> which
do not support the <code class="xref py py-attr docutils literal"><span class="pre">buffer</span></code> attribute.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.__stdin__">
<code class="descclassname">sys.</code><code class="descname">__stdin__</code><a class="headerlink" href="#sys.__stdin__" title="Permalink to this definition">¶</a></dt>
<dt id="sys.__stdout__">
<code class="descclassname">sys.</code><code class="descname">__stdout__</code><a class="headerlink" href="#sys.__stdout__" title="Permalink to this definition">¶</a></dt>
<dt id="sys.__stderr__">
<code class="descclassname">sys.</code><code class="descname">__stderr__</code><a class="headerlink" href="#sys.__stderr__" title="Permalink to this definition">¶</a></dt>
<dd><p>These objects contain the original values of <code class="docutils literal"><span class="pre">stdin</span></code>, <code class="docutils literal"><span class="pre">stderr</span></code> and
<code class="docutils literal"><span class="pre">stdout</span></code> at the start of the program. They are used during finalization,
and could be useful to print to the actual standard stream no matter if the
<code class="docutils literal"><span class="pre">sys.std*</span></code> object has been redirected.</p>
<p>It can also be used to restore the actual files to known working file objects
in case they have been overwritten with a broken object. However, the
preferred way to do this is to explicitly save the previous stream before
replacing it, and restore the saved object.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Under some conditions <code class="docutils literal"><span class="pre">stdin</span></code>, <code class="docutils literal"><span class="pre">stdout</span></code> and <code class="docutils literal"><span class="pre">stderr</span></code> as well as the
original values <code class="docutils literal"><span class="pre">__stdin__</span></code>, <code class="docutils literal"><span class="pre">__stdout__</span></code> and <code class="docutils literal"><span class="pre">__stderr__</span></code> can be
<code class="docutils literal"><span class="pre">None</span></code>. It is usually the case for Windows GUI apps that aren’t connected
to a console and Python apps started with <strong class="program">pythonw</strong>.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.thread_info">
<code class="descclassname">sys.</code><code class="descname">thread_info</code><a class="headerlink" href="#sys.thread_info" title="Permalink to this definition">¶</a></dt>
<dd><p>A <a class="reference internal" href="../glossary.html#term-struct-sequence"><span class="xref std std-term">struct sequence</span></a> holding information about the thread
implementation.</p>
<table border="1" class="docutils">
<colgroup>
<col width="24%" />
<col width="76%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Attribute</th>
<th class="head">Explanation</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="xref py py-const docutils literal"><span class="pre">name</span></code></td>
<td><p class="first">Name of the thread implementation:</p>
<blockquote class="last">
<div><ul class="simple">
<li><code class="docutils literal"><span class="pre">'nt'</span></code>: Windows threads</li>
<li><code class="docutils literal"><span class="pre">'pthread'</span></code>: POSIX threads</li>
<li><code class="docutils literal"><span class="pre">'solaris'</span></code>: Solaris threads</li>
</ul>
</div></blockquote>
</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal"><span class="pre">lock</span></code></td>
<td><p class="first">Name of the lock implementation:</p>
<blockquote class="last">
<div><ul class="simple">
<li><code class="docutils literal"><span class="pre">'semaphore'</span></code>: a lock uses a semaphore</li>
<li><code class="docutils literal"><span class="pre">'mutex+cond'</span></code>: a lock uses a mutex
and a condition variable</li>
<li><code class="docutils literal"><span class="pre">None</span></code> if this information is unknown</li>
</ul>
</div></blockquote>
</td>
</tr>
<tr class="row-even"><td><a class="reference internal" href="#sys.version" title="sys.version"><code class="xref py py-const docutils literal"><span class="pre">version</span></code></a></td>
<td>Name and version of the thread library. It is a string,
or <code class="docutils literal"><span class="pre">None</span></code> if these informations are unknown.</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.3.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.tracebacklimit">
<code class="descclassname">sys.</code><code class="descname">tracebacklimit</code><a class="headerlink" href="#sys.tracebacklimit" title="Permalink to this definition">¶</a></dt>
<dd><p>When this variable is set to an integer value, it determines the maximum number
of levels of traceback information printed when an unhandled exception occurs.
The default is <code class="docutils literal"><span class="pre">1000</span></code>. When set to <code class="docutils literal"><span class="pre">0</span></code> or less, all traceback information
is suppressed and only the exception type and value are printed.</p>
</dd></dl>
<dl class="data">
<dt id="sys.version">
<code class="descclassname">sys.</code><code class="descname">version</code><a class="headerlink" href="#sys.version" title="Permalink to this definition">¶</a></dt>
<dd><p>A string containing the version number of the Python interpreter plus additional
information on the build number and compiler used. This string is displayed
when the interactive interpreter is started. Do not extract version information
out of it, rather, use <a class="reference internal" href="#sys.version_info" title="sys.version_info"><code class="xref py py-data docutils literal"><span class="pre">version_info</span></code></a> and the functions provided by the
<a class="reference internal" href="platform.html#module-platform" title="platform: Retrieves as much platform identifying data as possible."><code class="xref py py-mod docutils literal"><span class="pre">platform</span></code></a> module.</p>
</dd></dl>
<dl class="data">
<dt id="sys.api_version">
<code class="descclassname">sys.</code><code class="descname">api_version</code><a class="headerlink" href="#sys.api_version" title="Permalink to this definition">¶</a></dt>
<dd><p>The C API version for this interpreter. Programmers may find this useful when
debugging version conflicts between Python and extension modules.</p>
</dd></dl>
<dl class="data">
<dt id="sys.version_info">
<code class="descclassname">sys.</code><code class="descname">version_info</code><a class="headerlink" href="#sys.version_info" title="Permalink to this definition">¶</a></dt>
<dd><p>A tuple containing the five components of the version number: <em>major</em>, <em>minor</em>,
<em>micro</em>, <em>releaselevel</em>, and <em>serial</em>. All values except <em>releaselevel</em> are
integers; the release level is <code class="docutils literal"><span class="pre">'alpha'</span></code>, <code class="docutils literal"><span class="pre">'beta'</span></code>, <code class="docutils literal"><span class="pre">'candidate'</span></code>, or
<code class="docutils literal"><span class="pre">'final'</span></code>. The <code class="docutils literal"><span class="pre">version_info</span></code> value corresponding to the Python version 2.0
is <code class="docutils literal"><span class="pre">(2,</span> <span class="pre">0,</span> <span class="pre">0,</span> <span class="pre">'final',</span> <span class="pre">0)</span></code>. The components can also be accessed by name,
so <code class="docutils literal"><span class="pre">sys.version_info[0]</span></code> is equivalent to <code class="docutils literal"><span class="pre">sys.version_info.major</span></code>
and so on.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.1: </span>Added named component attributes.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="sys.warnoptions">
<code class="descclassname">sys.</code><code class="descname">warnoptions</code><a class="headerlink" href="#sys.warnoptions" title="Permalink to this definition">¶</a></dt>
<dd><p>This is an implementation detail of the warnings framework; do not modify this
value. Refer to the <a class="reference internal" href="warnings.html#module-warnings" title="warnings: Issue warning messages and control their disposition."><code class="xref py py-mod docutils literal"><span class="pre">warnings</span></code></a> module for more information on the warnings
framework.</p>
</dd></dl>
<dl class="data">
<dt id="sys.winver">
<code class="descclassname">sys.</code><code class="descname">winver</code><a class="headerlink" href="#sys.winver" title="Permalink to this definition">¶</a></dt>
<dd><p>The version number used to form registry keys on Windows platforms. This is
stored as string resource 1000 in the Python DLL. The value is normally the
first three characters of <a class="reference internal" href="#sys.version" title="sys.version"><code class="xref py py-const docutils literal"><span class="pre">version</span></code></a>. It is provided in the <a class="reference internal" href="#module-sys" title="sys: Access system-specific parameters and functions."><code class="xref py py-mod docutils literal"><span class="pre">sys</span></code></a>
module for informational purposes; modifying this value has no effect on the
registry keys used by Python. Availability: Windows.</p>
</dd></dl>
<dl class="data">
<dt id="sys._xoptions">
<code class="descclassname">sys.</code><code class="descname">_xoptions</code><a class="headerlink" href="#sys._xoptions" title="Permalink to this definition">¶</a></dt>
<dd><p>A dictionary of the various implementation-specific flags passed through
the <a class="reference internal" href="../using/cmdline.html#cmdoption-X"><code class="xref std std-option docutils literal"><span class="pre">-X</span></code></a> command-line option. Option names are either mapped to
their values, if given explicitly, or to <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal"><span class="pre">True</span></code></a>. Example:</p>
<div class="highlight-shell-session"><div class="highlight"><pre><span></span><span class="gp">$</span> ./python -Xa<span class="o">=</span>b -Xc
<span class="go">Python 3.2a3+ (py3k, Oct 16 2010, 20:14:50)</span>
<span class="go">[GCC 4.4.3] on linux2</span>
<span class="go">Type "help", "copyright", "credits" or "license" for more information.</span>
<span class="gp">></span>>> import sys
<span class="gp">></span>>> sys._xoptions
<span class="go">{'a': 'b', 'c': True}</span>
</pre></div>
</div>
<div class="impl-detail compound">
<p><strong>CPython implementation detail:</strong> This is a CPython-specific way of accessing options passed through
<a class="reference internal" href="../using/cmdline.html#cmdoption-X"><code class="xref std std-option docutils literal"><span class="pre">-X</span></code></a>. Other implementations may export them through other
means, or not at all.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.2.</span></p>
</div>
</dd></dl>
<p class="rubric">Citations</p>
<table class="docutils citation" frame="void" id="c99" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id1">[C99]</a></td><td>ISO/IEC 9899:1999. “Programming languages – C.” A public draft of this standard is available at <a class="reference external" href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf">http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf</a>.</td></tr>
</tbody>
</table>
</div>
</div>
</div>
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