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<div class="section" id="module-posix">
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<span id="posix-the-most-common-posix-system-calls"></span><h1><a class="reference internal" href="#module-posix" title="posix: The most common POSIX system calls (normally used via module os). (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code></a> — The most common POSIX system calls<a class="headerlink" href="#module-posix" title="Permalink to this headline">¶</a></h1>
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<hr class="docutils" />
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<p>This module provides access to operating system functionality that is
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standardized by the C Standard and the POSIX standard (a thinly disguised Unix
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interface).</p>
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<p id="index-0"><strong>Do not import this module directly.</strong> Instead, import the module <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a>,
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which provides a <em>portable</em> version of this interface. On Unix, the <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a>
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module provides a superset of the <a class="reference internal" href="#module-posix" title="posix: The most common POSIX system calls (normally used via module os). (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code></a> interface. On non-Unix operating
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systems the <a class="reference internal" href="#module-posix" title="posix: The most common POSIX system calls (normally used via module os). (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code></a> module is not available, but a subset is always
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available through the <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> interface. Once <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> is imported, there is
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<em>no</em> performance penalty in using it instead of <a class="reference internal" href="#module-posix" title="posix: The most common POSIX system calls (normally used via module os). (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code></a>. In addition,
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<a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> provides some additional functionality, such as automatically calling
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<a class="reference internal" href="os.html#os.putenv" title="os.putenv"><code class="xref py py-func docutils literal notranslate"><span class="pre">putenv()</span></code></a> when an entry in <code class="docutils literal notranslate"><span class="pre">os.environ</span></code> is changed.</p>
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<p>Errors are reported as exceptions; the usual exceptions are given for type
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errors, while errors reported by the system calls raise <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a>.</p>
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<div class="section" id="large-file-support">
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<span id="posix-large-files"></span><h2>Large File Support<a class="headerlink" href="#large-file-support" title="Permalink to this headline">¶</a></h2>
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<p id="index-1">Several operating systems (including AIX, HP-UX, Irix and Solaris) provide
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support for files that are larger than 2 GiB from a C programming model where
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<code class="xref c c-type docutils literal notranslate"><span class="pre">int</span></code> and <code class="xref c c-type docutils literal notranslate"><span class="pre">long</span></code> are 32-bit values. This is typically accomplished
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by defining the relevant size and offset types as 64-bit values. Such files are
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sometimes referred to as <em class="dfn">large files</em>.</p>
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<p>Large file support is enabled in Python when the size of an <code class="xref c c-type docutils literal notranslate"><span class="pre">off_t</span></code> is
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larger than a <code class="xref c c-type docutils literal notranslate"><span class="pre">long</span></code> and the <code class="xref c c-type docutils literal notranslate"><span class="pre">long</span> <span class="pre">long</span></code> type is available and is
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at least as large as an <code class="xref c c-type docutils literal notranslate"><span class="pre">off_t</span></code>.
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It may be necessary to configure and compile Python with certain compiler flags
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to enable this mode. For example, it is enabled by default with recent versions
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of Irix, but with Solaris 2.6 and 2.7 you need to do something like:</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">CFLAGS</span><span class="o">=</span><span class="s2">"`getconf LFS_CFLAGS`"</span> <span class="n">OPT</span><span class="o">=</span><span class="s2">"-g -O2 $CFLAGS"</span> \
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<span class="o">./</span><span class="n">configure</span>
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</pre></div>
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</div>
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<p>On large-file-capable Linux systems, this might work:</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">CFLAGS</span><span class="o">=</span><span class="s1">'-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64'</span> <span class="n">OPT</span><span class="o">=</span><span class="s2">"-g -O2 $CFLAGS"</span> \
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<span class="o">./</span><span class="n">configure</span>
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</pre></div>
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</div>
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</div>
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<div class="section" id="notable-module-contents">
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<span id="posix-contents"></span><h2>Notable Module Contents<a class="headerlink" href="#notable-module-contents" title="Permalink to this headline">¶</a></h2>
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<p>In addition to many functions described in the <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> module documentation,
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<a class="reference internal" href="#module-posix" title="posix: The most common POSIX system calls (normally used via module os). (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code></a> defines the following data item:</p>
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<dl class="data">
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<dt id="posix.environ">
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<code class="descclassname">posix.</code><code class="descname">environ</code><a class="headerlink" href="#posix.environ" title="Permalink to this definition">¶</a></dt>
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<dd><p>A dictionary representing the string environment at the time the interpreter
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was started. Keys and values are bytes on Unix and str on Windows. For
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example, <code class="docutils literal notranslate"><span class="pre">environ[b'HOME']</span></code> (<code class="docutils literal notranslate"><span class="pre">environ['HOME']</span></code> on Windows) is the
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pathname of your home directory, equivalent to <code class="docutils literal notranslate"><span class="pre">getenv("HOME")</span></code> in C.</p>
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<p>Modifying this dictionary does not affect the string environment passed on by
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<a class="reference internal" href="os.html#os.execv" title="os.execv"><code class="xref py py-func docutils literal notranslate"><span class="pre">execv()</span></code></a>, <a class="reference internal" href="os.html#os.popen" title="os.popen"><code class="xref py py-func docutils literal notranslate"><span class="pre">popen()</span></code></a> or <a class="reference internal" href="os.html#os.system" title="os.system"><code class="xref py py-func docutils literal notranslate"><span class="pre">system()</span></code></a>; if you need to
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change the environment, pass <code class="docutils literal notranslate"><span class="pre">environ</span></code> to <a class="reference internal" href="os.html#os.execve" title="os.execve"><code class="xref py py-func docutils literal notranslate"><span class="pre">execve()</span></code></a> or add
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variable assignments and export statements to the command string for
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<a class="reference internal" href="os.html#os.system" title="os.system"><code class="xref py py-func docutils literal notranslate"><span class="pre">system()</span></code></a> or <a class="reference internal" href="os.html#os.popen" title="os.popen"><code class="xref py py-func docutils literal notranslate"><span class="pre">popen()</span></code></a>.</p>
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<div class="versionchanged">
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<p><span class="versionmodified changed">Changed in version 3.2: </span>On Unix, keys and values are bytes.</p>
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</div>
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<div class="admonition note">
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<p class="admonition-title">Note</p>
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<p>The <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> module provides an alternate implementation of <code class="docutils literal notranslate"><span class="pre">environ</span></code>
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which updates the environment on modification. Note also that updating
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<a class="reference internal" href="os.html#os.environ" title="os.environ"><code class="xref py py-data docutils literal notranslate"><span class="pre">os.environ</span></code></a> will render this dictionary obsolete. Use of the
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<a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> module version of this is recommended over direct access to the
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<a class="reference internal" href="#module-posix" title="posix: The most common POSIX system calls (normally used via module os). (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code></a> module.</p>
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<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">posix</span></code> — The most common POSIX system calls</a><ul>
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<li><a class="reference internal" href="#large-file-support">Large File Support</a></li>
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<li><a class="reference internal" href="#notable-module-contents">Notable Module Contents</a></li>
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