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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="X-UA-Compatible" content="IE=Edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>36.12. posixfile — File-like objects with locking support — Python 2.7.18 documentation</title> <link rel="stylesheet" href="../_static/classic.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/language_data.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 2.7.18 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="36.13. resource — Resource usage information" href="resource.html" /> <link rel="prev" title="36.11. pipes — Interface to shell pipelines" href="pipes.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="file:///usr/share/doc/python2.7/html/library/posixfile.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <div id="outdated-warning" style="padding: .5em; text-align: center; background-color: #FFBABA; color: #6A0E0E;"> This document is for an old version of Python that is <a href="https://devguide.python.org/devcycle/#end-of-life-branches">no longer supported</a>. 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Unix Specific Services</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <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 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 border="1" class="docutils"> <colgroup> <col width="15%" /> <col width="85%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Format</th> <th class="head">Meaning</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">u</span></code></td> <td>unlock the specified region</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">r</span></code></td> <td>request a read lock for the specified section</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">w</span></code></td> <td>request a write lock for the specified section</td> </tr> </tbody> </table> <p>In addition the following modifiers can be added to the format:</p> <table border="1" class="docutils"> <colgroup> <col width="20%" /> <col width="65%" /> <col width="14%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Modifier</th> <th class="head">Meaning</th> <th class="head">Notes</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">|</span></code></td> <td>wait until the lock has been granted</td> <td> </td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">?</span></code></td> <td>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.</td> <td>(1)</td> </tr> </tbody> </table> <p>Note:</p> <ol class="arabic simple"> <li>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.</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 border="1" class="docutils"> <colgroup> <col width="15%" /> <col width="85%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Format</th> <th class="head">Meaning</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">a</span></code></td> <td>append only flag</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">c</span></code></td> <td>close on exec flag</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">n</span></code></td> <td>no delay flag (also called non-blocking flag)</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">s</span></code></td> <td>synchronization flag</td> </tr> </tbody> </table> <p>In addition the following modifiers can be added to the format:</p> <table border="1" class="docutils"> <colgroup> <col width="20%" /> <col width="66%" /> <col width="14%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Modifier</th> <th class="head">Meaning</th> <th class="head">Notes</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">!</span></code></td> <td>turn the specified flags ‘off’, instead of the default ‘on’</td> <td>(1)</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">=</span></code></td> <td>replace the flags, instead of the default ‘OR’ operation</td> <td>(1)</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">?</span></code></td> <td>return a string in which the characters represent the flags that are set.</td> <td>(2)</td> </tr> </tbody> </table> <p>Notes:</p> <ol class="arabic simple"> <li>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.</li> <li>This string represents the flags after they may have been altered by the same call.</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> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h4>Previous topic</h4> <p class="topless"><a href="pipes.html" title="previous chapter">36.11. <code class="docutils literal notranslate"><span class="pre">pipes</span></code> — Interface to shell pipelines</a></p> <h4>Next topic</h4> <p class="topless"><a href="resource.html" title="next chapter">36.13. <code class="docutils literal notranslate"><span class="pre">resource</span></code> — Resource usage information</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul 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