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<div class="section" id="module-io">
<span id="io-core-tools-for-working-with-streams"></span><h1>15.2. <a class="reference internal" href="#module-io" title="io: Core tools for working with streams."><tt class="xref py py-mod docutils literal"><span class="pre">io</span></tt></a> — Core tools for working with streams<a class="headerlink" href="#module-io" title="Permalink to this headline">¶</a></h1>
<div class="section" id="overview">
<span id="io-overview"></span><h2>15.2.1. Overview<a class="headerlink" href="#overview" title="Permalink to this headline">¶</a></h2>
<p>The <a class="reference internal" href="#module-io" title="io: Core tools for working with streams."><tt class="xref py py-mod docutils literal"><span class="pre">io</span></tt></a> module provides Python’s main facilities for dealing for various
types of I/O. There are three main types of I/O: <em>text I/O</em>, <em>binary I/O</em>, <em>raw
I/O</em>. These are generic categories, and various backing stores can be used for
each of them. Concrete objects belonging to any of these categories will often
be called <em>streams</em>; another common term is <em>file-like objects</em>.</p>
<p>Independently of its category, each concrete stream object will also have
various capabilities: it can be read-only, write-only, or read-write. It can
also allow arbitrary random access (seeking forwards or backwards to any
location), or only sequential access (for example in the case of a socket or
pipe).</p>
<p>All streams are careful about the type of data you give to them. For example
giving a <a class="reference internal" href="functions.html#str" title="str"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a> object to the <tt class="docutils literal"><span class="pre">write()</span></tt> method of a binary stream
will raise a <tt class="docutils literal"><span class="pre">TypeError</span></tt>. So will giving a <a class="reference internal" href="functions.html#bytes" title="bytes"><tt class="xref py py-class docutils literal"><span class="pre">bytes</span></tt></a> object to the
<tt class="docutils literal"><span class="pre">write()</span></tt> method of a text stream.</p>
<div class="section" id="text-i-o">
<h3>15.2.1.1. Text I/O<a class="headerlink" href="#text-i-o" title="Permalink to this headline">¶</a></h3>
<p>Text I/O expects and produces <a class="reference internal" href="functions.html#str" title="str"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a> objects. This means that whenever
the backing store is natively made of bytes (such as in the case of a file),
encoding and decoding of data is made transparently as well as optional
translation of platform-specific newline characters.</p>
<p>The easiest way to create a text stream is with <a class="reference internal" href="functions.html#open" title="open"><tt class="xref py py-meth docutils literal"><span class="pre">open()</span></tt></a>, optionally
specifying an encoding:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">f</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="s">"myfile.txt"</span><span class="p">,</span> <span class="s">"r"</span><span class="p">,</span> <span class="n">encoding</span><span class="o">=</span><span class="s">"utf-8"</span><span class="p">)</span>
</pre></div>
</div>
<p>In-memory text streams are also available as <a class="reference internal" href="#io.StringIO" title="io.StringIO"><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a> objects:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">f</span> <span class="o">=</span> <span class="n">io</span><span class="o">.</span><span class="n">StringIO</span><span class="p">(</span><span class="s">"some initial text data"</span><span class="p">)</span>
</pre></div>
</div>
<p>The text stream API is described in detail in the documentation for the
<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a>.</p>
</div>
<div class="section" id="binary-i-o">
<h3>15.2.1.2. Binary I/O<a class="headerlink" href="#binary-i-o" title="Permalink to this headline">¶</a></h3>
<p>Binary I/O (also called <em>buffered I/O</em>) expects and produces <a class="reference internal" href="functions.html#bytes" title="bytes"><tt class="xref py py-class docutils literal"><span class="pre">bytes</span></tt></a>
objects. No encoding, decoding, or newline translation is performed. This
category of streams can be used for all kinds of non-text data, and also when
manual control over the handling of text data is desired.</p>
<p>The easiest way to create a binary stream is with <a class="reference internal" href="functions.html#open" title="open"><tt class="xref py py-meth docutils literal"><span class="pre">open()</span></tt></a> with <tt class="docutils literal"><span class="pre">'b'</span></tt> in
the mode string:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">f</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="s">"myfile.jpg"</span><span class="p">,</span> <span class="s">"rb"</span><span class="p">)</span>
</pre></div>
</div>
<p>In-memory binary streams are also available as <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><tt class="xref py py-class docutils literal"><span class="pre">BytesIO</span></tt></a> objects:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">f</span> <span class="o">=</span> <span class="n">io</span><span class="o">.</span><span class="n">BytesIO</span><span class="p">(</span><span class="n">b</span><span class="s">"some initial binary data: </span><span class="se">\x00\x01</span><span class="s">"</span><span class="p">)</span>
</pre></div>
</div>
<p>The binary stream API is described in detail in the docs of
<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>.</p>
<p>Other library modules may provide additional ways to create text or binary
streams. See <a class="reference internal" href="socket.html#socket.socket.makefile" title="socket.socket.makefile"><tt class="xref py py-meth docutils literal"><span class="pre">socket.socket.makefile()</span></tt></a> for example.</p>
</div>
<div class="section" id="raw-i-o">
<h3>15.2.1.3. Raw I/O<a class="headerlink" href="#raw-i-o" title="Permalink to this headline">¶</a></h3>
<p>Raw I/O (also called <em>unbuffered I/O</em>) is generally used as a low-level
building-block for binary and text streams; it is rarely useful to directly
manipulate a raw stream from user code. Nevertheless, you can create a raw
stream by opening a file in binary mode with buffering disabled:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">f</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="s">"myfile.jpg"</span><span class="p">,</span> <span class="s">"rb"</span><span class="p">,</span> <span class="n">buffering</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
</pre></div>
</div>
<p>The raw stream API is described in detail in the docs of <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a>.</p>
</div>
</div>
<div class="section" id="high-level-module-interface">
<h2>15.2.2. High-level Module Interface<a class="headerlink" href="#high-level-module-interface" title="Permalink to this headline">¶</a></h2>
<dl class="data">
<dt id="io.DEFAULT_BUFFER_SIZE">
<tt class="descclassname">io.</tt><tt class="descname">DEFAULT_BUFFER_SIZE</tt><a class="headerlink" href="#io.DEFAULT_BUFFER_SIZE" title="Permalink to this definition">¶</a></dt>
<dd><p>An int containing the default buffer size used by the module’s buffered I/O
classes. <a class="reference internal" href="functions.html#open" title="open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> uses the file’s blksize (as obtained by
<a class="reference internal" href="os.html#os.stat" title="os.stat"><tt class="xref py py-func docutils literal"><span class="pre">os.stat()</span></tt></a>) if possible.</p>
</dd></dl>
<dl class="function">
<dt id="io.open">
<tt class="descclassname">io.</tt><tt class="descname">open</tt><big>(</big><em>file</em>, <em>mode='r'</em>, <em>buffering=-1</em>, <em>encoding=None</em>, <em>errors=None</em>, <em>newline=None</em>, <em>closefd=True</em><big>)</big><a class="headerlink" href="#io.open" title="Permalink to this definition">¶</a></dt>
<dd><p>This is an alias for the builtin <a class="reference internal" href="functions.html#open" title="open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> function.</p>
</dd></dl>
<dl class="exception">
<dt id="io.BlockingIOError">
<em class="property">exception </em><tt class="descclassname">io.</tt><tt class="descname">BlockingIOError</tt><a class="headerlink" href="#io.BlockingIOError" title="Permalink to this definition">¶</a></dt>
<dd><p>Error raised when blocking would occur on a non-blocking stream. It inherits
<a class="reference internal" href="exceptions.html#IOError" title="IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a>.</p>
<p>In addition to those of <a class="reference internal" href="exceptions.html#IOError" title="IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a>, <a class="reference internal" href="#io.BlockingIOError" title="io.BlockingIOError"><tt class="xref py py-exc docutils literal"><span class="pre">BlockingIOError</span></tt></a> has one
attribute:</p>
<dl class="attribute">
<dt id="io.BlockingIOError.characters_written">
<tt class="descname">characters_written</tt><a class="headerlink" href="#io.BlockingIOError.characters_written" title="Permalink to this definition">¶</a></dt>
<dd><p>An integer containing the number of characters written to the stream
before it blocked.</p>
</dd></dl>
</dd></dl>
<dl class="exception">
<dt id="io.UnsupportedOperation">
<em class="property">exception </em><tt class="descclassname">io.</tt><tt class="descname">UnsupportedOperation</tt><a class="headerlink" href="#io.UnsupportedOperation" title="Permalink to this definition">¶</a></dt>
<dd><p>An exception inheriting <a class="reference internal" href="exceptions.html#IOError" title="IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a> and <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a> that is raised
when an unsupported operation is called on a stream.</p>
</dd></dl>
<div class="section" id="in-memory-streams">
<h3>15.2.2.1. In-memory streams<a class="headerlink" href="#in-memory-streams" title="Permalink to this headline">¶</a></h3>
<p>It is also possible to use a <a class="reference internal" href="functions.html#str" title="str"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a> or <a class="reference internal" href="functions.html#bytes" title="bytes"><tt class="xref py py-class docutils literal"><span class="pre">bytes</span></tt></a>-like object as a
file for both reading and writing. For strings <a class="reference internal" href="#io.StringIO" title="io.StringIO"><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a> can be used
like a file opened in text mode. <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><tt class="xref py py-class docutils literal"><span class="pre">BytesIO</span></tt></a> can be used like a file
opened in binary mode. Both provide full read-write capabilities with random
access.</p>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><a class="reference internal" href="sys.html#module-sys" title="sys: Access system-specific parameters and functions."><tt class="xref py py-mod docutils literal"><span class="pre">sys</span></tt></a></dt>
<dd>contains the standard IO streams: <a class="reference internal" href="sys.html#sys.stdin" title="sys.stdin"><tt class="xref py py-data docutils literal"><span class="pre">sys.stdin</span></tt></a>, <a class="reference internal" href="sys.html#sys.stdout" title="sys.stdout"><tt class="xref py py-data docutils literal"><span class="pre">sys.stdout</span></tt></a>,
and <a class="reference internal" href="sys.html#sys.stderr" title="sys.stderr"><tt class="xref py py-data docutils literal"><span class="pre">sys.stderr</span></tt></a>.</dd>
</dl>
</div>
</div>
</div>
<div class="section" id="class-hierarchy">
<h2>15.2.3. Class hierarchy<a class="headerlink" href="#class-hierarchy" title="Permalink to this headline">¶</a></h2>
<p>The implementation of I/O streams is organized as a hierarchy of classes. First
<a class="reference internal" href="../glossary.html#term-abstract-base-class"><em class="xref std std-term">abstract base classes</em></a> (ABCs), which are used to
specify the various categories of streams, then concrete classes providing the
standard stream implementations.</p>
<blockquote>
<div><div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The abstract base classes also provide default implementations of some
methods in order to help implementation of concrete stream classes. For
example, <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> provides unoptimized implementations of
<tt class="docutils literal"><span class="pre">readinto()</span></tt> and <tt class="docutils literal"><span class="pre">readline()</span></tt>.</p>
</div>
</div></blockquote>
<p>At the top of the I/O hierarchy is the abstract base class <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>. It
defines the basic interface to a stream. Note, however, that there is no
separation between reading and writing to streams; implementations are allowed
to raise <a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><tt class="xref py py-exc docutils literal"><span class="pre">UnsupportedOperation</span></tt></a> if they do not support a given operation.</p>
<p>The <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> ABC extends <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>. It deals with the reading
and writing of bytes to a stream. <a class="reference internal" href="#io.FileIO" title="io.FileIO"><tt class="xref py py-class docutils literal"><span class="pre">FileIO</span></tt></a> subclasses <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a>
to provide an interface to files in the machine’s file system.</p>
<p>The <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> ABC deals with buffering on a raw byte stream
(<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a>). Its subclasses, <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a>,
<a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a>, and <a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRWPair</span></tt></a> buffer streams that are
readable, writable, and both readable and writable. <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRandom</span></tt></a>
provides a buffered interface to random access streams. Another
<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> subclass, <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><tt class="xref py py-class docutils literal"><span class="pre">BytesIO</span></tt></a>, is a stream of in-memory
bytes.</p>
<p>The <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> ABC, another subclass of <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>, deals with
streams whose bytes represent text, and handles encoding and decoding to and
from strings. <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">TextIOWrapper</span></tt></a>, which extends it, is a buffered text
interface to a buffered raw stream (<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>). Finally,
<a class="reference internal" href="#io.StringIO" title="io.StringIO"><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a> is an in-memory stream for text.</p>
<p>Argument names are not part of the specification, and only the arguments of
<a class="reference internal" href="functions.html#open" title="open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> are intended to be used as keyword arguments.</p>
<div class="section" id="i-o-base-classes">
<h3>15.2.3.1. I/O Base Classes<a class="headerlink" href="#i-o-base-classes" title="Permalink to this headline">¶</a></h3>
<dl class="class">
<dt id="io.IOBase">
<em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">IOBase</tt><a class="headerlink" href="#io.IOBase" title="Permalink to this definition">¶</a></dt>
<dd><p>The abstract base class for all I/O classes, acting on streams of bytes.
There is no public constructor.</p>
<p>This class provides empty abstract implementations for many methods
that derived classes can override selectively; the default
implementations represent a file that cannot be read, written or
seeked.</p>
<p>Even though <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a> does not declare <tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt>, <tt class="xref py py-meth docutils literal"><span class="pre">readinto()</span></tt>,
or <tt class="xref py py-meth docutils literal"><span class="pre">write()</span></tt> because their signatures will vary, implementations and
clients should consider those methods part of the interface. Also,
implementations may raise a <a class="reference internal" href="exceptions.html#IOError" title="IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a> when operations they do not
support are called.</p>
<p>The basic type used for binary data read from or written to a file is
<a class="reference internal" href="functions.html#bytes" title="bytes"><tt class="xref py py-class docutils literal"><span class="pre">bytes</span></tt></a>. <a class="reference internal" href="functions.html#bytearray" title="bytearray"><tt class="xref py py-class docutils literal"><span class="pre">bytearray</span></tt></a>s are accepted too, and in some cases
(such as <tt class="xref py py-class docutils literal"><span class="pre">readinto</span></tt>) required. Text I/O classes work with
<a class="reference internal" href="functions.html#str" title="str"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a> data.</p>
<p>Note that calling any method (even inquiries) on a closed stream is
undefined. Implementations may raise <a class="reference internal" href="exceptions.html#IOError" title="IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a> in this case.</p>
<p>IOBase (and its subclasses) support the iterator protocol, meaning that an
<a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a> object can be iterated over yielding the lines in a stream.
Lines are defined slightly differently depending on whether the stream is
a binary stream (yielding bytes), or a text stream (yielding character
strings). See <a class="reference internal" href="readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><tt class="xref py py-meth docutils literal"><span class="pre">readline()</span></tt></a> below.</p>
<p>IOBase is also a context manager and therefore supports the
<a class="reference internal" href="../reference/compound_stmts.html#with"><tt class="xref std std-keyword docutils literal"><span class="pre">with</span></tt></a> statement. In this example, <em>file</em> is closed after the
<a class="reference internal" href="../reference/compound_stmts.html#with"><tt class="xref std std-keyword docutils literal"><span class="pre">with</span></tt></a> statement’s suite is finished—even if an exception occurs:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s">'spam.txt'</span><span class="p">,</span> <span class="s">'w'</span><span class="p">)</span> <span class="k">as</span> <span class="n">file</span><span class="p">:</span>
<span class="n">file</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s">'Spam and eggs!'</span><span class="p">)</span>
</pre></div>
</div>
<p><a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a> provides these data attributes and methods:</p>
<dl class="method">
<dt id="io.IOBase.close">
<tt class="descname">close</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.close" title="Permalink to this definition">¶</a></dt>
<dd><p>Flush and close this stream. This method has no effect if the file is
already closed. Once the file is closed, any operation on the file
(e.g. reading or writing) will raise a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a>.</p>
<p>As a convenience, it is allowed to call this method more than once;
only the first call, however, will have an effect.</p>
</dd></dl>
<dl class="attribute">
<dt id="io.IOBase.closed">
<tt class="descname">closed</tt><a class="headerlink" href="#io.IOBase.closed" title="Permalink to this definition">¶</a></dt>
<dd><p>True if the stream is closed.</p>
</dd></dl>
<dl class="method">
<dt id="io.IOBase.fileno">
<tt class="descname">fileno</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.fileno" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the underlying file descriptor (an integer) of the stream if it
exists. An <a class="reference internal" href="exceptions.html#IOError" title="IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a> is raised if the IO object does not use a file
descriptor.</p>
</dd></dl>
<dl class="method">
<dt id="io.IOBase.flush">
<tt class="descname">flush</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.flush" title="Permalink to this definition">¶</a></dt>
<dd><p>Flush the write buffers of the stream if applicable. This does nothing
for read-only and non-blocking streams.</p>
</dd></dl>
<dl class="method">
<dt id="io.IOBase.isatty">
<tt class="descname">isatty</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.isatty" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <tt class="xref docutils literal"><span class="pre">True</span></tt> if the stream is interactive (i.e., connected to
a terminal/tty device).</p>
</dd></dl>
<dl class="method">
<dt id="io.IOBase.readable">
<tt class="descname">readable</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.readable" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <tt class="xref docutils literal"><span class="pre">True</span></tt> if the stream can be read from. If False, <tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt>
will raise <a class="reference internal" href="exceptions.html#IOError" title="IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a>.</p>
</dd></dl>
<dl class="method">
<dt id="io.IOBase.readline">
<tt class="descname">readline</tt><big>(</big><em>limit=-1</em><big>)</big><a class="headerlink" href="#io.IOBase.readline" title="Permalink to this definition">¶</a></dt>
<dd><p>Read and return one line from the stream. If <em>limit</em> is specified, at
most <em>limit</em> bytes will be read.</p>
<p>The line terminator is always <tt class="docutils literal"><span class="pre">b'\n'</span></tt> for binary files; for text files,
the <em>newlines</em> argument to <a class="reference internal" href="functions.html#open" title="open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> can be used to select the line
terminator(s) recognized.</p>
</dd></dl>
<dl class="method">
<dt id="io.IOBase.readlines">
<tt class="descname">readlines</tt><big>(</big><em>hint=-1</em><big>)</big><a class="headerlink" href="#io.IOBase.readlines" title="Permalink to this definition">¶</a></dt>
<dd><p>Read and return a list of lines from the stream. <em>hint</em> can be specified
to control the number of lines read: no more lines will be read if the
total size (in bytes/characters) of all lines so far exceeds <em>hint</em>.</p>
</dd></dl>
<dl class="method">
<dt id="io.IOBase.seek">
<tt class="descname">seek</tt><big>(</big><em>offset</em>, <em>whence=SEEK_SET</em><big>)</big><a class="headerlink" href="#io.IOBase.seek" title="Permalink to this definition">¶</a></dt>
<dd><p>Change the stream position to the given byte <em>offset</em>. <em>offset</em> is
interpreted relative to the position indicated by <em>whence</em>. Values for
<em>whence</em> are:</p>
<ul class="simple">
<li><tt class="xref py py-data docutils literal"><span class="pre">SEEK_SET</span></tt> or <tt class="docutils literal"><span class="pre">0</span></tt> – start of the stream (the default);
<em>offset</em> should be zero or positive</li>
<li><tt class="xref py py-data docutils literal"><span class="pre">SEEK_CUR</span></tt> or <tt class="docutils literal"><span class="pre">1</span></tt> – current stream position; <em>offset</em> may
be negative</li>
<li><tt class="xref py py-data docutils literal"><span class="pre">SEEK_END</span></tt> or <tt class="docutils literal"><span class="pre">2</span></tt> – end of the stream; <em>offset</em> is usually
negative</li>
</ul>
<p>Return the new absolute position.</p>
<p class="versionadded">
<span class="versionmodified">New in version 3.1: </span>The <tt class="docutils literal"><span class="pre">SEEK_*</span></tt> constants.</p>
</dd></dl>
<dl class="method">
<dt id="io.IOBase.seekable">
<tt class="descname">seekable</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.seekable" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <tt class="xref docutils literal"><span class="pre">True</span></tt> if the stream supports random access. If <tt class="xref docutils literal"><span class="pre">False</span></tt>,
<a class="reference internal" href="#io.IOBase.seek" title="io.IOBase.seek"><tt class="xref py py-meth docutils literal"><span class="pre">seek()</span></tt></a>, <a class="reference internal" href="#io.IOBase.tell" title="io.IOBase.tell"><tt class="xref py py-meth docutils literal"><span class="pre">tell()</span></tt></a> and <a class="reference internal" href="#io.IOBase.truncate" title="io.IOBase.truncate"><tt class="xref py py-meth docutils literal"><span class="pre">truncate()</span></tt></a> will raise <a class="reference internal" href="exceptions.html#IOError" title="IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a>.</p>
</dd></dl>
<dl class="method">
<dt id="io.IOBase.tell">
<tt class="descname">tell</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.tell" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current stream position.</p>
</dd></dl>
<dl class="method">
<dt id="io.IOBase.truncate">
<tt class="descname">truncate</tt><big>(</big><em>size=None</em><big>)</big><a class="headerlink" href="#io.IOBase.truncate" title="Permalink to this definition">¶</a></dt>
<dd><p>Resize the stream to the given <em>size</em> in bytes (or the current position
if <em>size</em> is not specified). The current stream position isn’t changed.
This resizing can extend or reduce the current file size. In case of
extension, the contents of the new file area depend on the platform
(on most systems, additional bytes are zero-filled, on Windows they’re
undetermined). The new file size is returned.</p>
</dd></dl>
<dl class="method">
<dt id="io.IOBase.writable">
<tt class="descname">writable</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.writable" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <tt class="xref docutils literal"><span class="pre">True</span></tt> if the stream supports writing. If <tt class="xref docutils literal"><span class="pre">False</span></tt>,
<tt class="xref py py-meth docutils literal"><span class="pre">write()</span></tt> and <a class="reference internal" href="#io.IOBase.truncate" title="io.IOBase.truncate"><tt class="xref py py-meth docutils literal"><span class="pre">truncate()</span></tt></a> will raise <a class="reference internal" href="exceptions.html#IOError" title="IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a>.</p>
</dd></dl>
<dl class="method">
<dt id="io.IOBase.writelines">
<tt class="descname">writelines</tt><big>(</big><em>lines</em><big>)</big><a class="headerlink" href="#io.IOBase.writelines" title="Permalink to this definition">¶</a></dt>
<dd><p>Write a list of lines to the stream. Line separators are not added, so it
is usual for each of the lines provided to have a line separator at the
end.</p>
</dd></dl>
</dd></dl>
<dl class="class">
<dt id="io.RawIOBase">
<em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">RawIOBase</tt><a class="headerlink" href="#io.RawIOBase" title="Permalink to this definition">¶</a></dt>
<dd><p>Base class for raw binary I/O. It inherits <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>. There is no
public constructor.</p>
<p>Raw binary I/O typically provides low-level access to an underlying OS
device or API, and does not try to encapsulate it in high-level primitives
(this is left to Buffered I/O and Text I/O, described later in this page).</p>
<p>In addition to the attributes and methods from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>,
RawIOBase provides the following methods:</p>
<dl class="method">
<dt id="io.RawIOBase.read">
<tt class="descname">read</tt><big>(</big><em>n=-1</em><big>)</big><a class="headerlink" href="#io.RawIOBase.read" title="Permalink to this definition">¶</a></dt>
<dd><p>Read up to <em>n</em> bytes from the object and return them. As a convenience,
if <em>n</em> is unspecified or -1, <a class="reference internal" href="#io.RawIOBase.readall" title="io.RawIOBase.readall"><tt class="xref py py-meth docutils literal"><span class="pre">readall()</span></tt></a> is called. Otherwise,
only one system call is ever made. Fewer than <em>n</em> bytes may be
returned if the operating system call returns fewer than <em>n</em> bytes.</p>
<p>If 0 bytes are returned, and <em>n</em> was not 0, this indicates end of file.
If the object is in non-blocking mode and no bytes are available,
<tt class="xref docutils literal"><span class="pre">None</span></tt> is returned.</p>
</dd></dl>
<dl class="method">
<dt id="io.RawIOBase.readall">
<tt class="descname">readall</tt><big>(</big><big>)</big><a class="headerlink" href="#io.RawIOBase.readall" title="Permalink to this definition">¶</a></dt>
<dd><p>Read and return all the bytes from the stream until EOF, using multiple
calls to the stream if necessary.</p>
</dd></dl>
<dl class="method">
<dt id="io.RawIOBase.readinto">
<tt class="descname">readinto</tt><big>(</big><em>b</em><big>)</big><a class="headerlink" href="#io.RawIOBase.readinto" title="Permalink to this definition">¶</a></dt>
<dd><p>Read up to len(b) bytes into bytearray <em>b</em> and return the number
of bytes read. If the object is in non-blocking mode and no
bytes are available, <tt class="xref docutils literal"><span class="pre">None</span></tt> is returned.</p>
</dd></dl>
<dl class="method">
<dt id="io.RawIOBase.write">
<tt class="descname">write</tt><big>(</big><em>b</em><big>)</big><a class="headerlink" href="#io.RawIOBase.write" title="Permalink to this definition">¶</a></dt>
<dd><p>Write the given bytes or bytearray object, <em>b</em>, to the underlying raw
stream and return the number of bytes written. This can be less than
<tt class="docutils literal"><span class="pre">len(b)</span></tt>, depending on specifics of the underlying raw stream, and
especially if it is in non-blocking mode. <tt class="xref docutils literal"><span class="pre">None</span></tt> is returned if the
raw stream is set not to block and no single byte could be readily
written to it.</p>
</dd></dl>
</dd></dl>
<dl class="class">
<dt id="io.BufferedIOBase">
<em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">BufferedIOBase</tt><a class="headerlink" href="#io.BufferedIOBase" title="Permalink to this definition">¶</a></dt>
<dd><p>Base class for binary streams that support some kind of buffering.
It inherits <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>. There is no public constructor.</p>
<p>The main difference with <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> is that methods <a class="reference internal" href="#io.BufferedIOBase.read" title="io.BufferedIOBase.read"><tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt></a>,
<a class="reference internal" href="#io.BufferedIOBase.readinto" title="io.BufferedIOBase.readinto"><tt class="xref py py-meth docutils literal"><span class="pre">readinto()</span></tt></a> and <a class="reference internal" href="#io.BufferedIOBase.write" title="io.BufferedIOBase.write"><tt class="xref py py-meth docutils literal"><span class="pre">write()</span></tt></a> will try (respectively) to read as much
input as requested or to consume all given output, at the expense of
making perhaps more than one system call.</p>
<p>In addition, those methods can raise <a class="reference internal" href="#io.BlockingIOError" title="io.BlockingIOError"><tt class="xref py py-exc docutils literal"><span class="pre">BlockingIOError</span></tt></a> if the
underlying raw stream is in non-blocking mode and cannot take or give
enough data; unlike their <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> counterparts, they will
never return <tt class="xref docutils literal"><span class="pre">None</span></tt>.</p>
<p>Besides, the <a class="reference internal" href="#io.BufferedIOBase.read" title="io.BufferedIOBase.read"><tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt></a> method does not have a default
implementation that defers to <a class="reference internal" href="#io.BufferedIOBase.readinto" title="io.BufferedIOBase.readinto"><tt class="xref py py-meth docutils literal"><span class="pre">readinto()</span></tt></a>.</p>
<p>A typical <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> implementation should not inherit from a
<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> implementation, but wrap one, like
<a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a> and <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a> do.</p>
<p><a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> provides or overrides these methods and attribute in
addition to those from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>:</p>
<dl class="attribute">
<dt id="io.BufferedIOBase.raw">
<tt class="descname">raw</tt><a class="headerlink" href="#io.BufferedIOBase.raw" title="Permalink to this definition">¶</a></dt>
<dd><p>The underlying raw stream (a <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> instance) that
<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> deals with. This is not part of the
<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> API and may not exist on some implementations.</p>
</dd></dl>
<dl class="method">
<dt id="io.BufferedIOBase.detach">
<tt class="descname">detach</tt><big>(</big><big>)</big><a class="headerlink" href="#io.BufferedIOBase.detach" title="Permalink to this definition">¶</a></dt>
<dd><p>Separate the underlying raw stream from the buffer and return it.</p>
<p>After the raw stream has been detached, the buffer is in an unusable
state.</p>
<p>Some buffers, like <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><tt class="xref py py-class docutils literal"><span class="pre">BytesIO</span></tt></a>, do not have the concept of a single
raw stream to return from this method. They raise
<a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><tt class="xref py py-exc docutils literal"><span class="pre">UnsupportedOperation</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 3.1.</span></p>
</dd></dl>
<dl class="method">
<dt id="io.BufferedIOBase.read">
<tt class="descname">read</tt><big>(</big><em>n=-1</em><big>)</big><a class="headerlink" href="#io.BufferedIOBase.read" title="Permalink to this definition">¶</a></dt>
<dd><p>Read and return up to <em>n</em> bytes. If the argument is omitted, <tt class="xref docutils literal"><span class="pre">None</span></tt>, or
negative, data is read and returned until EOF is reached. An empty bytes
object is returned if the stream is already at EOF.</p>
<p>If the argument is positive, and the underlying raw stream is not
interactive, multiple raw reads may be issued to satisfy the byte count
(unless EOF is reached first). But for interactive raw streams, at most
one raw read will be issued, and a short result does not imply that EOF is
imminent.</p>
<p>A <a class="reference internal" href="#io.BlockingIOError" title="io.BlockingIOError"><tt class="xref py py-exc docutils literal"><span class="pre">BlockingIOError</span></tt></a> is raised if the underlying raw stream is in
non blocking-mode, and has no data available at the moment.</p>
</dd></dl>
<dl class="method">
<dt id="io.BufferedIOBase.read1">
<tt class="descname">read1</tt><big>(</big><em>n=-1</em><big>)</big><a class="headerlink" href="#io.BufferedIOBase.read1" title="Permalink to this definition">¶</a></dt>
<dd><p>Read and return up to <em>n</em> bytes, with at most one call to the underlying
raw stream’s <a class="reference internal" href="#io.RawIOBase.read" title="io.RawIOBase.read"><tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt></a> method. This can be useful if you
are implementing your own buffering on top of a <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>
object.</p>
</dd></dl>
<dl class="method">
<dt id="io.BufferedIOBase.readinto">
<tt class="descname">readinto</tt><big>(</big><em>b</em><big>)</big><a class="headerlink" href="#io.BufferedIOBase.readinto" title="Permalink to this definition">¶</a></dt>
<dd><p>Read up to len(b) bytes into bytearray <em>b</em> and return the number of bytes
read.</p>
<p>Like <a class="reference internal" href="#io.BufferedIOBase.read" title="io.BufferedIOBase.read"><tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt></a>, multiple reads may be issued to the underlying raw
stream, unless the latter is ‘interactive’.</p>
<p>A <a class="reference internal" href="#io.BlockingIOError" title="io.BlockingIOError"><tt class="xref py py-exc docutils literal"><span class="pre">BlockingIOError</span></tt></a> is raised if the underlying raw stream is in
non blocking-mode, and has no data available at the moment.</p>
</dd></dl>
<dl class="method">
<dt id="io.BufferedIOBase.write">
<tt class="descname">write</tt><big>(</big><em>b</em><big>)</big><a class="headerlink" href="#io.BufferedIOBase.write" title="Permalink to this definition">¶</a></dt>
<dd><p>Write the given bytes or bytearray object, <em>b</em> and return the number
of bytes written (never less than <tt class="docutils literal"><span class="pre">len(b)</span></tt>, since if the write fails
an <a class="reference internal" href="exceptions.html#IOError" title="IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a> will be raised). Depending on the actual
implementation, these bytes may be readily written to the underlying
stream, or held in a buffer for performance and latency reasons.</p>
<p>When in non-blocking mode, a <a class="reference internal" href="#io.BlockingIOError" title="io.BlockingIOError"><tt class="xref py py-exc docutils literal"><span class="pre">BlockingIOError</span></tt></a> is raised if the
data needed to be written to the raw stream but it couldn’t accept
all the data without blocking.</p>
</dd></dl>
</dd></dl>
</div>
<div class="section" id="raw-file-i-o">
<h3>15.2.3.2. Raw File I/O<a class="headerlink" href="#raw-file-i-o" title="Permalink to this headline">¶</a></h3>
<dl class="class">
<dt id="io.FileIO">
<em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">FileIO</tt><big>(</big><em>name</em>, <em>mode='r'</em>, <em>closefd=True</em><big>)</big><a class="headerlink" href="#io.FileIO" title="Permalink to this definition">¶</a></dt>
<dd><p><a class="reference internal" href="#io.FileIO" title="io.FileIO"><tt class="xref py py-class docutils literal"><span class="pre">FileIO</span></tt></a> represents an OS-level file containing bytes data.
It implements the <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> interface (and therefore the
<a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a> interface, too).</p>
<p>The <em>name</em> can be one of two things:</p>
<ul class="simple">
<li>a character string or bytes object representing the path to the file
which will be opened;</li>
<li>an integer representing the number of an existing OS-level file descriptor
to which the resulting <a class="reference internal" href="#io.FileIO" title="io.FileIO"><tt class="xref py py-class docutils literal"><span class="pre">FileIO</span></tt></a> object will give access.</li>
</ul>
<p>The <em>mode</em> can be <tt class="docutils literal"><span class="pre">'r'</span></tt>, <tt class="docutils literal"><span class="pre">'w'</span></tt> or <tt class="docutils literal"><span class="pre">'a'</span></tt> for reading (default), writing,
or appending. The file will be created if it doesn’t exist when opened for
writing or appending; it will be truncated when opened for writing. Add a
<tt class="docutils literal"><span class="pre">'+'</span></tt> to the mode to allow simultaneous reading and writing.</p>
<p>The <tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt> (when called with a positive argument), <tt class="xref py py-meth docutils literal"><span class="pre">readinto()</span></tt>
and <tt class="xref py py-meth docutils literal"><span class="pre">write()</span></tt> methods on this class will only make one system call.</p>
<p>In addition to the attributes and methods from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a> and
<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a>, <a class="reference internal" href="#io.FileIO" title="io.FileIO"><tt class="xref py py-class docutils literal"><span class="pre">FileIO</span></tt></a> provides the following data
attributes and methods:</p>
<dl class="attribute">
<dt id="io.FileIO.mode">
<tt class="descname">mode</tt><a class="headerlink" href="#io.FileIO.mode" title="Permalink to this definition">¶</a></dt>
<dd><p>The mode as given in the constructor.</p>
</dd></dl>
<dl class="attribute">
<dt id="io.FileIO.name">
<tt class="descname">name</tt><a class="headerlink" href="#io.FileIO.name" title="Permalink to this definition">¶</a></dt>
<dd><p>The file name. This is the file descriptor of the file when no name is
given in the constructor.</p>
</dd></dl>
</dd></dl>
</div>
<div class="section" id="buffered-streams">
<h3>15.2.3.3. Buffered Streams<a class="headerlink" href="#buffered-streams" title="Permalink to this headline">¶</a></h3>
<p>Buffered I/O streams provide a higher-level interface to an I/O device
than raw I/O does.</p>
<dl class="class">
<dt id="io.BytesIO">
<em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">BytesIO</tt><big>(</big><span class="optional">[</span><em>initial_bytes</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#io.BytesIO" title="Permalink to this definition">¶</a></dt>
<dd><p>A stream implementation using an in-memory bytes buffer. It inherits
<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>.</p>
<p>The argument <em>initial_bytes</em> contains optional initial <a class="reference internal" href="functions.html#bytes" title="bytes"><tt class="xref py py-class docutils literal"><span class="pre">bytes</span></tt></a> data.</p>
<p><a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><tt class="xref py py-class docutils literal"><span class="pre">BytesIO</span></tt></a> provides or overrides these methods in addition to those
from <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> and <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>:</p>
<dl class="method">
<dt id="io.BytesIO.getbuffer">
<tt class="descname">getbuffer</tt><big>(</big><big>)</big><a class="headerlink" href="#io.BytesIO.getbuffer" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a readable and writable view over the contents of the buffer
without copying them. Also, mutating the view will transparently
update the contents of the buffer:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">b</span> <span class="o">=</span> <span class="n">io</span><span class="o">.</span><span class="n">BytesIO</span><span class="p">(</span><span class="n">b</span><span class="s">"abcdef"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">view</span> <span class="o">=</span> <span class="n">b</span><span class="o">.</span><span class="n">getbuffer</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">view</span><span class="p">[</span><span class="mi">2</span><span class="p">:</span><span class="mi">4</span><span class="p">]</span> <span class="o">=</span> <span class="n">b</span><span class="s">"56"</span>
<span class="gp">>>> </span><span class="n">b</span><span class="o">.</span><span class="n">getvalue</span><span class="p">()</span>
<span class="go">b'ab56ef'</span>
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">As long as the view exists, the <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><tt class="xref py py-class docutils literal"><span class="pre">BytesIO</span></tt></a> object cannot be
resized.</p>
</div>
<p class="versionadded">
<span class="versionmodified">New in version 3.2.</span></p>
</dd></dl>
<dl class="method">
<dt id="io.BytesIO.getvalue">
<tt class="descname">getvalue</tt><big>(</big><big>)</big><a class="headerlink" href="#io.BytesIO.getvalue" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <tt class="docutils literal"><span class="pre">bytes</span></tt> containing the entire contents of the buffer.</p>
</dd></dl>
<dl class="method">
<dt id="io.BytesIO.read1">
<tt class="descname">read1</tt><big>(</big><big>)</big><a class="headerlink" href="#io.BytesIO.read1" title="Permalink to this definition">¶</a></dt>
<dd><p>In <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><tt class="xref py py-class docutils literal"><span class="pre">BytesIO</span></tt></a>, this is the same as <tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt>.</p>
</dd></dl>
</dd></dl>
<dl class="class">
<dt id="io.BufferedReader">
<em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">BufferedReader</tt><big>(</big><em>raw</em>, <em>buffer_size=DEFAULT_BUFFER_SIZE</em><big>)</big><a class="headerlink" href="#io.BufferedReader" title="Permalink to this definition">¶</a></dt>
<dd><p>A buffer providing higher-level access to a readable, sequential
<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> object. It inherits <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>.
When reading data from this object, a larger amount of data may be
requested from the underlying raw stream, and kept in an internal buffer.
The buffered data can then be returned directly on subsequent reads.</p>
<p>The constructor creates a <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a> for the given readable
<em>raw</em> stream and <em>buffer_size</em>. If <em>buffer_size</em> is omitted,
<a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><tt class="xref py py-data docutils literal"><span class="pre">DEFAULT_BUFFER_SIZE</span></tt></a> is used.</p>
<p><a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a> provides or overrides these methods in addition to
those from <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> and <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>:</p>
<dl class="method">
<dt id="io.BufferedReader.peek">
<tt class="descname">peek</tt><big>(</big><span class="optional">[</span><em>n</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#io.BufferedReader.peek" title="Permalink to this definition">¶</a></dt>
<dd><p>Return bytes from the stream without advancing the position. At most one
single read on the raw stream is done to satisfy the call. The number of
bytes returned may be less or more than requested.</p>
</dd></dl>
<dl class="method">
<dt id="io.BufferedReader.read">
<tt class="descname">read</tt><big>(</big><span class="optional">[</span><em>n</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#io.BufferedReader.read" title="Permalink to this definition">¶</a></dt>
<dd><p>Read and return <em>n</em> bytes, or if <em>n</em> is not given or negative, until EOF
or if the read call would block in non-blocking mode.</p>
</dd></dl>
<dl class="method">
<dt id="io.BufferedReader.read1">
<tt class="descname">read1</tt><big>(</big><em>n</em><big>)</big><a class="headerlink" href="#io.BufferedReader.read1" title="Permalink to this definition">¶</a></dt>
<dd><p>Read and return up to <em>n</em> bytes with only one call on the raw stream. If
at least one byte is buffered, only buffered bytes are returned.
Otherwise, one raw stream read call is made.</p>
</dd></dl>
</dd></dl>
<dl class="class">
<dt id="io.BufferedWriter">
<em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">BufferedWriter</tt><big>(</big><em>raw</em>, <em>buffer_size=DEFAULT_BUFFER_SIZE</em><big>)</big><a class="headerlink" href="#io.BufferedWriter" title="Permalink to this definition">¶</a></dt>
<dd><p>A buffer providing higher-level access to a writeable, sequential
<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> object. It inherits <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>.
When writing to this object, data is normally held into an internal
buffer. The buffer will be written out to the underlying <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a>
object under various conditions, including:</p>
<ul class="simple">
<li>when the buffer gets too small for all pending data;</li>
<li>when <a class="reference internal" href="#io.BufferedWriter.flush" title="io.BufferedWriter.flush"><tt class="xref py py-meth docutils literal"><span class="pre">flush()</span></tt></a> is called;</li>
<li>when a <tt class="xref py py-meth docutils literal"><span class="pre">seek()</span></tt> is requested (for <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRandom</span></tt></a> objects);</li>
<li>when the <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a> object is closed or destroyed.</li>
</ul>
<p>The constructor creates a <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a> for the given writeable
<em>raw</em> stream. If the <em>buffer_size</em> is not given, it defaults to
<a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><tt class="xref py py-data docutils literal"><span class="pre">DEFAULT_BUFFER_SIZE</span></tt></a>.</p>
<p>A third argument, <em>max_buffer_size</em>, is supported, but unused and deprecated.</p>
<p><a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a> provides or overrides these methods in addition to
those from <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> and <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>:</p>
<dl class="method">
<dt id="io.BufferedWriter.flush">
<tt class="descname">flush</tt><big>(</big><big>)</big><a class="headerlink" href="#io.BufferedWriter.flush" title="Permalink to this definition">¶</a></dt>
<dd><p>Force bytes held in the buffer into the raw stream. A
<a class="reference internal" href="#io.BlockingIOError" title="io.BlockingIOError"><tt class="xref py py-exc docutils literal"><span class="pre">BlockingIOError</span></tt></a> should be raised if the raw stream blocks.</p>
</dd></dl>
<dl class="method">
<dt id="io.BufferedWriter.write">
<tt class="descname">write</tt><big>(</big><em>b</em><big>)</big><a class="headerlink" href="#io.BufferedWriter.write" title="Permalink to this definition">¶</a></dt>
<dd><p>Write the bytes or bytearray object, <em>b</em> and return the number of bytes
written. When in non-blocking mode, a <a class="reference internal" href="#io.BlockingIOError" title="io.BlockingIOError"><tt class="xref py py-exc docutils literal"><span class="pre">BlockingIOError</span></tt></a> is raised
if the buffer needs to be written out but the raw stream blocks.</p>
</dd></dl>
</dd></dl>
<dl class="class">
<dt id="io.BufferedRandom">
<em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">BufferedRandom</tt><big>(</big><em>raw</em>, <em>buffer_size=DEFAULT_BUFFER_SIZE</em><big>)</big><a class="headerlink" href="#io.BufferedRandom" title="Permalink to this definition">¶</a></dt>
<dd><p>A buffered interface to random access streams. It inherits
<a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a> and <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a>, and further supports
<tt class="xref py py-meth docutils literal"><span class="pre">seek()</span></tt> and <tt class="xref py py-meth docutils literal"><span class="pre">tell()</span></tt> functionality.</p>
<p>The constructor creates a reader and writer for a seekable raw stream, given
in the first argument. If the <em>buffer_size</em> is omitted it defaults to
<a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><tt class="xref py py-data docutils literal"><span class="pre">DEFAULT_BUFFER_SIZE</span></tt></a>.</p>
<p>A third argument, <em>max_buffer_size</em>, is supported, but unused and deprecated.</p>
<p><a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRandom</span></tt></a> is capable of anything <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a> or
<a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a> can do.</p>
</dd></dl>
<dl class="class">
<dt id="io.BufferedRWPair">
<em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">BufferedRWPair</tt><big>(</big><em>reader</em>, <em>writer</em>, <em>buffer_size=DEFAULT_BUFFER_SIZE</em><big>)</big><a class="headerlink" href="#io.BufferedRWPair" title="Permalink to this definition">¶</a></dt>
<dd><p>A buffered I/O object combining two unidirectional <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a>
objects – one readable, the other writeable – into a single bidirectional
endpoint. It inherits <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>.</p>
<p><em>reader</em> and <em>writer</em> are <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> objects that are readable and
writeable respectively. If the <em>buffer_size</em> is omitted it defaults to
<a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><tt class="xref py py-data docutils literal"><span class="pre">DEFAULT_BUFFER_SIZE</span></tt></a>.</p>
<p>A fourth argument, <em>max_buffer_size</em>, is supported, but unused and
deprecated.</p>
<p><a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRWPair</span></tt></a> implements all of <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>‘s methods
except for <a class="reference internal" href="#io.BufferedIOBase.detach" title="io.BufferedIOBase.detach"><tt class="xref py py-meth docutils literal"><span class="pre">detach()</span></tt></a>, which raises
<a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><tt class="xref py py-exc docutils literal"><span class="pre">UnsupportedOperation</span></tt></a>.</p>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last"><a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRWPair</span></tt></a> does not attempt to synchronize accesses to
its underlying raw streams. You should not pass it the same object
as reader and writer; use <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRandom</span></tt></a> instead.</p>
</div>
</dd></dl>
</div>
<div class="section" id="id1">
<h3>15.2.3.4. Text I/O<a class="headerlink" href="#id1" title="Permalink to this headline">¶</a></h3>
<dl class="class">
<dt id="io.TextIOBase">
<em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">TextIOBase</tt><a class="headerlink" href="#io.TextIOBase" title="Permalink to this definition">¶</a></dt>
<dd><p>Base class for text streams. This class provides a character and line based
interface to stream I/O. There is no <tt class="xref py py-meth docutils literal"><span class="pre">readinto()</span></tt> method because
Python’s character strings are immutable. It inherits <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>.
There is no public constructor.</p>
<p><a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> provides or overrides these data attributes and
methods in addition to those from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>:</p>
<dl class="attribute">
<dt id="io.TextIOBase.encoding">
<tt class="descname">encoding</tt><a class="headerlink" href="#io.TextIOBase.encoding" title="Permalink to this definition">¶</a></dt>
<dd><p>The name of the encoding used to decode the stream’s bytes into
strings, and to encode strings into bytes.</p>
</dd></dl>
<dl class="attribute">
<dt id="io.TextIOBase.errors">
<tt class="descname">errors</tt><a class="headerlink" href="#io.TextIOBase.errors" title="Permalink to this definition">¶</a></dt>
<dd><p>The error setting of the decoder or encoder.</p>
</dd></dl>
<dl class="attribute">
<dt id="io.TextIOBase.newlines">
<tt class="descname">newlines</tt><a class="headerlink" href="#io.TextIOBase.newlines" title="Permalink to this definition">¶</a></dt>
<dd><p>A string, a tuple of strings, or <tt class="xref docutils literal"><span class="pre">None</span></tt>, indicating the newlines
translated so far. Depending on the implementation and the initial
constructor flags, this may not be available.</p>
</dd></dl>
<dl class="attribute">
<dt id="io.TextIOBase.buffer">
<tt class="descname">buffer</tt><a class="headerlink" href="#io.TextIOBase.buffer" title="Permalink to this definition">¶</a></dt>
<dd><p>The underlying binary buffer (a <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> instance) that
<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> deals with. This is not part of the
<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> API and may not exist on some implementations.</p>
</dd></dl>
<dl class="method">
<dt id="io.TextIOBase.detach">
<tt class="descname">detach</tt><big>(</big><big>)</big><a class="headerlink" href="#io.TextIOBase.detach" title="Permalink to this definition">¶</a></dt>
<dd><p>Separate the underlying binary buffer from the <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> and
return it.</p>
<p>After the underlying buffer has been detached, the <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> is
in an unusable state.</p>
<p>Some <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> implementations, like <a class="reference internal" href="#io.StringIO" title="io.StringIO"><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a>, may not
have the concept of an underlying buffer and calling this method will
raise <a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><tt class="xref py py-exc docutils literal"><span class="pre">UnsupportedOperation</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 3.1.</span></p>
</dd></dl>
<dl class="method">
<dt id="io.TextIOBase.read">
<tt class="descname">read</tt><big>(</big><em>n</em><big>)</big><a class="headerlink" href="#io.TextIOBase.read" title="Permalink to this definition">¶</a></dt>
<dd><p>Read and return at most <em>n</em> characters from the stream as a single
<a class="reference internal" href="functions.html#str" title="str"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a>. If <em>n</em> is negative or <tt class="xref docutils literal"><span class="pre">None</span></tt>, reads until EOF.</p>
</dd></dl>
<dl class="method">
<dt id="io.TextIOBase.readline">
<tt class="descname">readline</tt><big>(</big><big>)</big><a class="headerlink" href="#io.TextIOBase.readline" title="Permalink to this definition">¶</a></dt>
<dd><p>Read until newline or EOF and return a single <tt class="docutils literal"><span class="pre">str</span></tt>. If the stream is
already at EOF, an empty string is returned.</p>
</dd></dl>
<dl class="method">
<dt id="io.TextIOBase.write">
<tt class="descname">write</tt><big>(</big><em>s</em><big>)</big><a class="headerlink" href="#io.TextIOBase.write" title="Permalink to this definition">¶</a></dt>
<dd><p>Write the string <em>s</em> to the stream and return the number of characters
written.</p>
</dd></dl>
</dd></dl>
<dl class="class">
<dt id="io.TextIOWrapper">
<em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">TextIOWrapper</tt><big>(</big><em>buffer</em>, <em>encoding=None</em>, <em>errors=None</em>, <em>newline=None</em>, <em>line_buffering=False</em><big>)</big><a class="headerlink" href="#io.TextIOWrapper" title="Permalink to this definition">¶</a></dt>
<dd><p>A buffered text stream over a <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> binary stream.
It inherits <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a>.</p>
<p><em>encoding</em> gives the name of the encoding that the stream will be decoded or
encoded with. It defaults to <a class="reference internal" href="locale.html#locale.getpreferredencoding" title="locale.getpreferredencoding"><tt class="xref py py-func docutils literal"><span class="pre">locale.getpreferredencoding()</span></tt></a>.</p>
<p><em>errors</em> is an optional string that specifies how encoding and decoding
errors are to be handled. Pass <tt class="docutils literal"><span class="pre">'strict'</span></tt> to raise a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a>
exception if there is an encoding error (the default of <tt class="xref docutils literal"><span class="pre">None</span></tt> has the same
effect), or pass <tt class="docutils literal"><span class="pre">'ignore'</span></tt> to ignore errors. (Note that ignoring encoding
errors can lead to data loss.) <tt class="docutils literal"><span class="pre">'replace'</span></tt> causes a replacement marker
(such as <tt class="docutils literal"><span class="pre">'?'</span></tt>) to be inserted where there is malformed data. When
writing, <tt class="docutils literal"><span class="pre">'xmlcharrefreplace'</span></tt> (replace with the appropriate XML character
reference) or <tt class="docutils literal"><span class="pre">'backslashreplace'</span></tt> (replace with backslashed escape
sequences) can be used. Any other error handling name that has been
registered with <a class="reference internal" href="codecs.html#codecs.register_error" title="codecs.register_error"><tt class="xref py py-func docutils literal"><span class="pre">codecs.register_error()</span></tt></a> is also valid.</p>
<p><em>newline</em> can be <tt class="xref docutils literal"><span class="pre">None</span></tt>, <tt class="docutils literal"><span class="pre">''</span></tt>, <tt class="docutils literal"><span class="pre">'\n'</span></tt>, <tt class="docutils literal"><span class="pre">'\r'</span></tt>, or <tt class="docutils literal"><span class="pre">'\r\n'</span></tt>. It
controls the handling of line endings. If it is <tt class="xref docutils literal"><span class="pre">None</span></tt>, universal newlines
is enabled. With this enabled, on input, the lines endings <tt class="docutils literal"><span class="pre">'\n'</span></tt>,
<tt class="docutils literal"><span class="pre">'\r'</span></tt>, or <tt class="docutils literal"><span class="pre">'\r\n'</span></tt> are translated to <tt class="docutils literal"><span class="pre">'\n'</span></tt> before being returned to
the caller. Conversely, on output, <tt class="docutils literal"><span class="pre">'\n'</span></tt> is translated to the system
default line separator, <a class="reference internal" href="os.html#os.linesep" title="os.linesep"><tt class="xref py py-data docutils literal"><span class="pre">os.linesep</span></tt></a>. If <em>newline</em> is any other of its
legal values, that newline becomes the newline when the file is read and it
is returned untranslated. On output, <tt class="docutils literal"><span class="pre">'\n'</span></tt> is converted to the <em>newline</em>.</p>
<p>If <em>line_buffering</em> is <tt class="xref docutils literal"><span class="pre">True</span></tt>, <tt class="xref py py-meth docutils literal"><span class="pre">flush()</span></tt> is implied when a call to
write contains a newline character.</p>
<p><a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">TextIOWrapper</span></tt></a> provides one attribute in addition to those of
<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> and its parents:</p>
<dl class="attribute">
<dt id="io.TextIOWrapper.line_buffering">
<tt class="descname">line_buffering</tt><a class="headerlink" href="#io.TextIOWrapper.line_buffering" title="Permalink to this definition">¶</a></dt>
<dd><p>Whether line buffering is enabled.</p>
</dd></dl>
</dd></dl>
<dl class="class">
<dt id="io.StringIO">
<em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">StringIO</tt><big>(</big><em>initial_value=''</em>, <em>newline=None</em><big>)</big><a class="headerlink" href="#io.StringIO" title="Permalink to this definition">¶</a></dt>
<dd><p>An in-memory stream for text I/O.</p>
<p>The initial value of the buffer (an empty string by default) can be set by
providing <em>initial_value</em>. The <em>newline</em> argument works like that of
<a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">TextIOWrapper</span></tt></a>. The default is to do no newline translation.</p>
<p><a class="reference internal" href="#io.StringIO" title="io.StringIO"><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a> provides this method in addition to those from
<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> and its parents:</p>
<dl class="method">
<dt id="io.StringIO.getvalue">
<tt class="descname">getvalue</tt><big>(</big><big>)</big><a class="headerlink" href="#io.StringIO.getvalue" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a <tt class="docutils literal"><span class="pre">str</span></tt> containing the entire contents of the buffer at any
time before the <a class="reference internal" href="#io.StringIO" title="io.StringIO"><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a> object’s <tt class="xref py py-meth docutils literal"><span class="pre">close()</span></tt> method is
called.</p>
</dd></dl>
<p>Example usage:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">io</span>
<span class="n">output</span> <span class="o">=</span> <span class="n">io</span><span class="o">.</span><span class="n">StringIO</span><span class="p">()</span>
<span class="n">output</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s">'First line.</span><span class="se">\n</span><span class="s">'</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s">'Second line.'</span><span class="p">,</span> <span class="n">file</span><span class="o">=</span><span class="n">output</span><span class="p">)</span>
<span class="c"># Retrieve file contents -- this will be</span>
<span class="c"># 'First line.\nSecond line.\n'</span>
<span class="n">contents</span> <span class="o">=</span> <span class="n">output</span><span class="o">.</span><span class="n">getvalue</span><span class="p">()</span>
<span class="c"># Close object and discard memory buffer --</span>
<span class="c"># .getvalue() will now raise an exception.</span>
<span class="n">output</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
</dd></dl>
<dl class="class">
<dt id="io.IncrementalNewlineDecoder">
<em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">IncrementalNewlineDecoder</tt><a class="headerlink" href="#io.IncrementalNewlineDecoder" title="Permalink to this definition">¶</a></dt>
<dd><p>A helper codec that decodes newlines for universal newlines mode. It
inherits <a class="reference internal" href="codecs.html#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><tt class="xref py py-class docutils literal"><span class="pre">codecs.IncrementalDecoder</span></tt></a>.</p>
</dd></dl>
</div>
</div>
<div class="section" id="performance">
<h2>15.2.4. Performance<a class="headerlink" href="#performance" title="Permalink to this headline">¶</a></h2>
<p>This section discusses the performance of the provided concrete I/O
implementations.</p>
<div class="section" id="id2">
<h3>15.2.4.1. Binary I/O<a class="headerlink" href="#id2" title="Permalink to this headline">¶</a></h3>
<p>By reading and writing only large chunks of data even when the user asks for a
single byte, buffered I/O hides any inefficiency in calling and executing the
operating system’s unbuffered I/O routines. The gain depends on the OS and the
kind of I/O which is performed. For example, on some modern OSes such as Linux,
unbuffered disk I/O can be as fast as buffered I/O. The bottom line, however,
is that buffered I/O offers predictable performance regardless of the platform
and the backing device. Therefore, it is most always preferable to use buffered
I/O rather than unbuffered I/O for binary datal</p>
</div>
<div class="section" id="id3">
<h3>15.2.4.2. Text I/O<a class="headerlink" href="#id3" title="Permalink to this headline">¶</a></h3>
<p>Text I/O over a binary storage (such as a file) is significantly slower than
binary I/O over the same storage, because it requires conversions between
unicode and binary data using a character codec. This can become noticeable
handling huge amounts of text data like large log files. Also,
<tt class="xref py py-meth docutils literal"><span class="pre">TextIOWrapper.tell()</span></tt> and <tt class="xref py py-meth docutils literal"><span class="pre">TextIOWrapper.seek()</span></tt> are both quite slow
due to the reconstruction algorithm used.</p>
<p><a class="reference internal" href="#io.StringIO" title="io.StringIO"><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a>, however, is a native in-memory unicode container and will
exhibit similar speed to <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><tt class="xref py py-class docutils literal"><span class="pre">BytesIO</span></tt></a>.</p>
</div>
<div class="section" id="multi-threading">
<h3>15.2.4.3. Multi-threading<a class="headerlink" href="#multi-threading" title="Permalink to this headline">¶</a></h3>
<p><a class="reference internal" href="#io.FileIO" title="io.FileIO"><tt class="xref py py-class docutils literal"><span class="pre">FileIO</span></tt></a> objects are thread-safe to the extent that the operating system
calls (such as <tt class="docutils literal"><span class="pre">read(2)</span></tt> under Unix) they wrap are thread-safe too.</p>
<p>Binary buffered objects (instances of <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a>,
<a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a>, <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRandom</span></tt></a> and <a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRWPair</span></tt></a>)
protect their internal structures using a lock; it is therefore safe to call
them from multiple threads at once.</p>
<p><a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">TextIOWrapper</span></tt></a> objects are not thread-safe.</p>
</div>
<div class="section" id="reentrancy">
<h3>15.2.4.4. Reentrancy<a class="headerlink" href="#reentrancy" title="Permalink to this headline">¶</a></h3>
<p>Binary buffered objects (instances of <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a>,
<a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a>, <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRandom</span></tt></a> and <a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRWPair</span></tt></a>)
are not reentrant. While reentrant calls will not happen in normal situations,
they can arise from doing I/O in a <a class="reference internal" href="signal.html#module-signal" title="signal: Set handlers for asynchronous events."><tt class="xref py py-mod docutils literal"><span class="pre">signal</span></tt></a> handler. If a thread tries to
renter a buffered object which it is already accessing, a <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><tt class="xref py py-exc docutils literal"><span class="pre">RuntimeError</span></tt></a> is
raised. Note this doesn’t prohibit a different thread from entering the
buffered object.</p>
<p>The above implicitly extends to text files, since the <a class="reference internal" href="functions.html#open" title="open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> function
will wrap a buffered object inside a <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">TextIOWrapper</span></tt></a>. This includes
standard streams and therefore affects the built-in function <a class="reference internal" href="functions.html#print" title="print"><tt class="xref py py-func docutils literal"><span class="pre">print()</span></tt></a> as
well.</p>
</div>
</div>
</div>
</div>
</div>
</div>
<div class="sphinxsidebar">
<div class="sphinxsidebarwrapper">
<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">15.2. <tt class="docutils literal"><span class="pre">io</span></tt> — Core tools for working with streams</a><ul>
<li><a class="reference internal" href="#overview">15.2.1. Overview</a><ul>
<li><a class="reference internal" href="#text-i-o">15.2.1.1. Text I/O</a></li>
<li><a class="reference internal" href="#binary-i-o">15.2.1.2. Binary I/O</a></li>
<li><a class="reference internal" href="#raw-i-o">15.2.1.3. Raw I/O</a></li>
</ul>
</li>
<li><a class="reference internal" href="#high-level-module-interface">15.2.2. High-level Module Interface</a><ul>
<li><a class="reference internal" href="#in-memory-streams">15.2.2.1. In-memory streams</a></li>
</ul>
</li>
<li><a class="reference internal" href="#class-hierarchy">15.2.3. Class hierarchy</a><ul>
<li><a class="reference internal" href="#i-o-base-classes">15.2.3.1. I/O Base Classes</a></li>
<li><a class="reference internal" href="#raw-file-i-o">15.2.3.2. Raw File I/O</a></li>
<li><a class="reference internal" href="#buffered-streams">15.2.3.3. Buffered Streams</a></li>
<li><a class="reference internal" href="#id1">15.2.3.4. Text I/O</a></li>
</ul>
</li>
<li><a class="reference internal" href="#performance">15.2.4. Performance</a><ul>
<li><a class="reference internal" href="#id2">15.2.4.1. Binary I/O</a></li>
<li><a class="reference internal" href="#id3">15.2.4.2. Text I/O</a></li>
<li><a class="reference internal" href="#multi-threading">15.2.4.3. Multi-threading</a></li>
<li><a class="reference internal" href="#reentrancy">15.2.4.4. Reentrancy</a></li>
</ul>
</li>
</ul>
</li>
</ul>
<h4>Previous topic</h4>
<p class="topless"><a href="os.html"
title="previous chapter">15.1. <tt class="docutils literal docutils literal"><span class="pre">os</span></tt> — Miscellaneous operating system interfaces</a></p>
<h4>Next topic</h4>
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distrib
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Mandriva
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2010.1
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x86_64
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media
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contrib-backports
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by-pkgid
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3ba3bd1608c672ba2129b098a48e9e4d
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files
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718
