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<div class="section" id="module-posixfile">
<span id="posixfile-file-like-objects-with-locking-support"></span><h1>36.12. <a class="reference internal" href="#module-posixfile" title="posixfile: A file-like object with support for locking. (deprecated) (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posixfile</span></code></a> — File-like objects with locking support<a class="headerlink" href="#module-posixfile" title="Permalink to this headline">¶</a></h1>
<div class="deprecated" id="index-0">
<p><span class="versionmodified deprecated">Deprecated since version 1.5: </span>The locking operation that this module provides is done better and more portably
by the <a class="reference internal" href="fcntl.html#fcntl.lockf" title="fcntl.lockf"><code class="xref py py-func docutils literal notranslate"><span class="pre">fcntl.lockf()</span></code></a> call.</p>
</div>
<p id="index-1">This module implements some additional functionality over the built-in file
objects. In particular, it implements file locking, control over the file
flags, and an easy interface to duplicate the file object. The module defines a
new file object, the posixfile object. It has all the standard file object
methods and adds the methods described below. This module only works for
certain flavors of Unix, since it uses <a class="reference internal" href="fcntl.html#fcntl.fcntl" title="fcntl.fcntl"><code class="xref py py-func docutils literal notranslate"><span class="pre">fcntl.fcntl()</span></code></a> for file locking.</p>
<p>To instantiate a posixfile object, use the <a class="reference internal" href="#posixfile.open" title="posixfile.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">posixfile.open()</span></code></a> function. The
resulting object looks and feels roughly the same as a standard file object.</p>
<p>The <a class="reference internal" href="#module-posixfile" title="posixfile: A file-like object with support for locking. (deprecated) (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posixfile</span></code></a> module defines the following constants:</p>
<dl class="data">
<dt id="posixfile.SEEK_SET">
<code class="descclassname">posixfile.</code><code class="descname">SEEK_SET</code><a class="headerlink" href="#posixfile.SEEK_SET" title="Permalink to this definition">¶</a></dt>
<dd><p>Offset is calculated from the start of the file.</p>
</dd></dl>
<dl class="data">
<dt id="posixfile.SEEK_CUR">
<code class="descclassname">posixfile.</code><code class="descname">SEEK_CUR</code><a class="headerlink" href="#posixfile.SEEK_CUR" title="Permalink to this definition">¶</a></dt>
<dd><p>Offset is calculated from the current position in the file.</p>
</dd></dl>
<dl class="data">
<dt id="posixfile.SEEK_END">
<code class="descclassname">posixfile.</code><code class="descname">SEEK_END</code><a class="headerlink" href="#posixfile.SEEK_END" title="Permalink to this definition">¶</a></dt>
<dd><p>Offset is calculated from the end of the file.</p>
</dd></dl>
<p>The <a class="reference internal" href="#module-posixfile" title="posixfile: A file-like object with support for locking. (deprecated) (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posixfile</span></code></a> module defines the following functions:</p>
<dl class="function">
<dt id="posixfile.open">
<code class="descclassname">posixfile.</code><code class="descname">open</code><span class="sig-paren">(</span><em>filename</em><span class="optional">[</span>, <em>mode</em><span class="optional">[</span>, <em>bufsize</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#posixfile.open" title="Permalink to this definition">¶</a></dt>
<dd><p>Create a new posixfile object with the given filename and mode. The <em>filename</em>,
<em>mode</em> and <em>bufsize</em> arguments are interpreted the same way as by the built-in
<a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> function.</p>
</dd></dl>
<dl class="function">
<dt id="posixfile.fileopen">
<code class="descclassname">posixfile.</code><code class="descname">fileopen</code><span class="sig-paren">(</span><em>fileobject</em><span class="sig-paren">)</span><a class="headerlink" href="#posixfile.fileopen" title="Permalink to this definition">¶</a></dt>
<dd><p>Create a new posixfile object with the given standard file object. The resulting
object has the same filename and mode as the original file object.</p>
</dd></dl>
<p>The posixfile object defines the following additional methods:</p>
<dl class="method">
<dt id="posixfile.posixfile.lock">
<code class="descclassname">posixfile.</code><code class="descname">lock</code><span class="sig-paren">(</span><em>fmt</em><span class="optional">[</span>, <em>len</em><span class="optional">[</span>, <em>start</em><span class="optional">[</span>, <em>whence</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#posixfile.posixfile.lock" title="Permalink to this definition">¶</a></dt>
<dd><p>Lock the specified section of the file that the file object is referring to.
The format is explained below in a table. The <em>len</em> argument specifies the
length of the section that should be locked. The default is <code class="docutils literal notranslate"><span class="pre">0</span></code>. <em>start</em>
specifies the starting offset of the section, where the default is <code class="docutils literal notranslate"><span class="pre">0</span></code>. The
<em>whence</em> argument specifies where the offset is relative to. It accepts one of
the constants <a class="reference internal" href="#posixfile.SEEK_SET" title="posixfile.SEEK_SET"><code class="xref py py-const docutils literal notranslate"><span class="pre">SEEK_SET</span></code></a>, <a class="reference internal" href="#posixfile.SEEK_CUR" title="posixfile.SEEK_CUR"><code class="xref py py-const docutils literal notranslate"><span class="pre">SEEK_CUR</span></code></a> or <a class="reference internal" href="#posixfile.SEEK_END" title="posixfile.SEEK_END"><code class="xref py py-const docutils literal notranslate"><span class="pre">SEEK_END</span></code></a>. The
default is <a class="reference internal" href="#posixfile.SEEK_SET" title="posixfile.SEEK_SET"><code class="xref py py-const docutils literal notranslate"><span class="pre">SEEK_SET</span></code></a>. For more information about the arguments refer to
the <em class="manpage">fcntl(2)</em> manual page on your system.</p>
</dd></dl>
<dl class="method">
<dt id="posixfile.posixfile.flags">
<code class="descclassname">posixfile.</code><code class="descname">flags</code><span class="sig-paren">(</span><span class="optional">[</span><em>flags</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#posixfile.posixfile.flags" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the specified flags for the file that the file object is referring to. The
new flags are ORed with the old flags, unless specified otherwise. The format
is explained below in a table. Without the <em>flags</em> argument a string indicating
the current flags is returned (this is the same as the <code class="docutils literal notranslate"><span class="pre">?</span></code> modifier). For
more information about the flags refer to the <em class="manpage">fcntl(2)</em> manual page on
your system.</p>
</dd></dl>
<dl class="method">
<dt id="posixfile.posixfile.dup">
<code class="descclassname">posixfile.</code><code class="descname">dup</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#posixfile.posixfile.dup" title="Permalink to this definition">¶</a></dt>
<dd><p>Duplicate the file object and the underlying file pointer and file descriptor.
The resulting object behaves as if it were newly opened.</p>
</dd></dl>
<dl class="method">
<dt id="posixfile.posixfile.dup2">
<code class="descclassname">posixfile.</code><code class="descname">dup2</code><span class="sig-paren">(</span><em>fd</em><span class="sig-paren">)</span><a class="headerlink" href="#posixfile.posixfile.dup2" title="Permalink to this definition">¶</a></dt>
<dd><p>Duplicate the file object and the underlying file pointer and file descriptor.
The new object will have the given file descriptor. Otherwise the resulting
object behaves as if it were newly opened.</p>
</dd></dl>
<dl class="method">
<dt id="posixfile.posixfile.file">
<code class="descclassname">posixfile.</code><code class="descname">file</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#posixfile.posixfile.file" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the standard file object that the posixfile object is based on. This is
sometimes necessary for functions that insist on a standard file object.</p>
</dd></dl>
<p>All methods raise <a class="reference internal" href="exceptions.html#exceptions.IOError" title="exceptions.IOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IOError</span></code></a> when the request fails.</p>
<p>Format characters for the <code class="xref py py-meth docutils literal notranslate"><span class="pre">lock()</span></code> method have the following meaning:</p>
<table class="docutils align-center">
<colgroup>
<col style="width: 15%" />
<col style="width: 85%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Format</p></th>
<th class="head"><p>Meaning</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">u</span></code></p></td>
<td><p>unlock the specified region</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">r</span></code></p></td>
<td><p>request a read lock for the specified section</p></td>
</tr>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">w</span></code></p></td>
<td><p>request a write lock for the specified
section</p></td>
</tr>
</tbody>
</table>
<p>In addition the following modifiers can be added to the format:</p>
<table class="docutils align-center">
<colgroup>
<col style="width: 20%" />
<col style="width: 65%" />
<col style="width: 14%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Modifier</p></th>
<th class="head"><p>Meaning</p></th>
<th class="head"><p>Notes</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">|</span></code></p></td>
<td><p>wait until the lock has been
granted</p></td>
<td></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">?</span></code></p></td>
<td><p>return the first lock
conflicting with the requested
lock, or <code class="docutils literal notranslate"><span class="pre">None</span></code> if there is
no conflict.</p></td>
<td><p>(1)</p></td>
</tr>
</tbody>
</table>
<p>Note:</p>
<ol class="arabic simple">
<li><p>The lock returned is in the format <code class="docutils literal notranslate"><span class="pre">(mode,</span> <span class="pre">len,</span> <span class="pre">start,</span> <span class="pre">whence,</span> <span class="pre">pid)</span></code> where
<em>mode</em> is a character representing the type of lock (‘r’ or ‘w’). This modifier
prevents a request from being granted; it is for query purposes only.</p></li>
</ol>
<p>Format characters for the <code class="xref py py-meth docutils literal notranslate"><span class="pre">flags()</span></code> method have the following meanings:</p>
<table class="docutils align-center">
<colgroup>
<col style="width: 15%" />
<col style="width: 85%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Format</p></th>
<th class="head"><p>Meaning</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">a</span></code></p></td>
<td><p>append only flag</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">c</span></code></p></td>
<td><p>close on exec flag</p></td>
</tr>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">n</span></code></p></td>
<td><p>no delay flag (also called non-blocking flag)</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">s</span></code></p></td>
<td><p>synchronization flag</p></td>
</tr>
</tbody>
</table>
<p>In addition the following modifiers can be added to the format:</p>
<table class="docutils align-center">
<colgroup>
<col style="width: 20%" />
<col style="width: 66%" />
<col style="width: 14%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Modifier</p></th>
<th class="head"><p>Meaning</p></th>
<th class="head"><p>Notes</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">!</span></code></p></td>
<td><p>turn the specified flags ‘off’,
instead of the default ‘on’</p></td>
<td><p>(1)</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">=</span></code></p></td>
<td><p>replace the flags, instead of
the default ‘OR’ operation</p></td>
<td><p>(1)</p></td>
</tr>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">?</span></code></p></td>
<td><p>return a string in which the
characters represent the flags
that are set.</p></td>
<td><p>(2)</p></td>
</tr>
</tbody>
</table>
<p>Notes:</p>
<ol class="arabic simple">
<li><p>The <code class="docutils literal notranslate"><span class="pre">!</span></code> and <code class="docutils literal notranslate"><span class="pre">=</span></code> modifiers are mutually exclusive.</p></li>
<li><p>This string represents the flags after they may have been altered by the same
call.</p></li>
</ol>
<p>Examples:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">posixfile</span>
<span class="n">file</span> <span class="o">=</span> <span class="n">posixfile</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s1">'testfile'</span><span class="p">,</span> <span class="s1">'w'</span><span class="p">)</span>
<span class="n">file</span><span class="o">.</span><span class="n">lock</span><span class="p">(</span><span class="s1">'w|'</span><span class="p">)</span>
<span class="o">...</span>
<span class="n">file</span><span class="o">.</span><span class="n">lock</span><span class="p">(</span><span class="s1">'u'</span><span class="p">)</span>
<span class="n">file</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
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