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Command line and environment</a><ul> <li><a class="reference internal" href="#command-line">1.1. Command line</a><ul> <li><a class="reference internal" href="#interface-options">1.1.1. Interface options</a></li> <li><a class="reference internal" href="#generic-options">1.1.2. Generic options</a></li> <li><a class="reference internal" href="#miscellaneous-options">1.1.3. Miscellaneous options</a></li> <li><a class="reference internal" href="#controlling-color">1.1.4. Controlling color</a></li> <li><a class="reference internal" href="#options-you-shouldn-t-use">1.1.5. Options you shouldn’t use</a></li> </ul> </li> <li><a class="reference internal" href="#environment-variables">1.2. Environment variables</a><ul> <li><a class="reference internal" href="#debug-mode-variables">1.2.1. Debug-mode variables</a></li> </ul> </li> </ul> </li> </ul> </div> <div> <h4>Previous topic</h4> <a href="index.html" title="previous chapter">Python Setup and Usage</a> </div> <div> <h4>Next topic</h4> <a href="unix.html" title="next chapter">2. Using Python on Unix platforms</a> </div> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/main/Doc/using/cmdline.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </nav> </div> </div> <div class="related" role="navigation" aria-label="Related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="unix.html" title="2. 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Command line and environment</a></li> <li class="right"> <div class="inline-search" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box" /> <input type="submit" value="Go" /> </form> </div> | </li> <li class="right"> <label class="theme-selector-label"> Theme <select class="theme-selector" oninput="activateTheme(this.value)"> <option value="auto" selected>Auto</option> <option value="light">Light</option> <option value="dark">Dark</option> </select> </label> |</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <section id="command-line-and-environment"> <h1>1. Command line and environment<a class="headerlink" href="#command-line-and-environment" title="Link to this heading">¶</a></h1> The CPython interpreter scans the command line and the environment for various settings. <div class="impl-detail compound"> CPython implementation detail: Other implementations’ command line schemes may differ. See <a class="reference internal" href="../reference/introduction.html#implementations">Alternate Implementations</a> for further resources. </div> <section id="command-line"> <h2>1.1. Command line<a class="headerlink" href="#command-line" title="Link to this heading">¶</a></h2> When invoking Python, you may specify any of these options: <div class="highlight-sh notranslate"><div class="highlight"><pre>python [-bBdEhiIOPqRsSuvVWx?] [-c command | -m module-name | script | - ] [args] </pre></div> </div> The most common use case is, of course, a simple invocation of a script: <div class="highlight-sh notranslate"><div class="highlight"><pre>python myscript.py </pre></div> </div> <section id="interface-options"> <h3>1.1.1. Interface options<a class="headerlink" href="#interface-options" title="Link to this heading">¶</a></h3> The interpreter interface resembles that of the UNIX shell, but provides some additional methods of invocation: <ul class="simple"> <li>When called with standard input connected to a tty device, it prompts for commands and executes them until an EOF (an end-of-file character, you can produce that with <kbd class="kbd compound docutils literal notranslate"><kbd class="kbd docutils literal notranslate">Ctrl</kbd>-<kbd class="kbd docutils literal notranslate">D</kbd></kbd> on UNIX or <kbd class="kbd compound docutils literal notranslate"><kbd class="kbd docutils literal notranslate">Ctrl</kbd>-<kbd class="kbd docutils literal notranslate">Z,</kbd> <kbd class="kbd docutils literal notranslate">Enter</kbd></kbd> on Windows) is read. For more on interactive mode, see <a class="reference internal" href="../tutorial/appendix.html#tut-interac">Interactive Mode</a>.</li> <li>When called with a file name argument or with a file as standard input, it reads and executes a script from that file.</li> <li>When called with a directory name argument, it reads and executes an appropriately named script from that directory.</li> <li>When called with <code class="docutils literal notranslate">-c command</code>, it executes the Python statement(s) given as command. Here command may contain multiple statements separated by newlines. Leading whitespace is significant in Python statements!</li> <li>When called with <code class="docutils literal notranslate">-m module-name</code>, the given module is located on the Python module path and executed as a script.</li> </ul> In non-interactive mode, the entire input is parsed before it is executed. An interface option terminates the list of options consumed by the interpreter, all consecutive arguments will end up in <a class="reference internal" href="../library/sys.html#sys.argv" title="sys.argv"><code class="xref py py-data docutils literal notranslate">sys.argv</code></a> – note that the first element, subscript zero (<code class="docutils literal notranslate">sys.argv[0]</code>), is a string reflecting the program’s source. <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-c"> -c <command><a class="headerlink" href="#cmdoption-c" title="Link to this definition">¶</a></dt> <dd>Execute the Python code in command. command can be one or more statements separated by newlines, with significant leading whitespace as in normal module code. If this option is given, the first element of <a class="reference internal" href="../library/sys.html#sys.argv" title="sys.argv"><code class="xref py py-data docutils literal notranslate">sys.argv</code></a> will be <code class="docutils literal notranslate">"-c"</code> and the current directory will be added to the start of <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a> (allowing modules in that directory to be imported as top level modules). Raises an <a class="reference internal" href="../library/sys.html#auditing">auditing event</a> <code class="docutils literal notranslate">cpython.run_command</code> with argument <code class="docutils literal notranslate">command</code>. </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-m"> -m <module-name><a class="headerlink" href="#cmdoption-m" title="Link to this definition">¶</a></dt> <dd>Search <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a> for the named module and execute its contents as the <a class="reference internal" href="../library/__main__.html#module-__main__" title="__main__: The environment where top-level code is run. Covers command-line interfaces, import-time behavior, and ``__name__ == '__main__'``."><code class="xref py py-mod docutils literal notranslate">__main__</code></a> module. Since the argument is a module name, you must not give a file extension (<code class="docutils literal notranslate">.py</code>). The module name should be a valid absolute Python module name, but the implementation may not always enforce this (e.g. it may allow you to use a name that includes a hyphen). Package names (including namespace packages) are also permitted. When a package name is supplied instead of a normal module, the interpreter will execute <code class="docutils literal notranslate"><pkg>.__main__</code> as the main module. This behaviour is deliberately similar to the handling of directories and zipfiles that are passed to the interpreter as the script argument. <div class="admonition note"> Note This option cannot be used with built-in modules and extension modules written in C, since they do not have Python module files. However, it can still be used for precompiled modules, even if the original source file is not available. </div> If this option is given, the first element of <a class="reference internal" href="../library/sys.html#sys.argv" title="sys.argv"><code class="xref py py-data docutils literal notranslate">sys.argv</code></a> will be the full path to the module file (while the module file is being located, the first element will be set to <code class="docutils literal notranslate">"-m"</code>). As with the <a class="reference internal" href="#cmdoption-c"><code class="xref std std-option docutils literal notranslate">-c</code></a> option, the current directory will be added to the start of <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a>. <a class="reference internal" href="#cmdoption-I"><code class="xref std std-option docutils literal notranslate">-I</code></a> option can be used to run the script in isolated mode where <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a> contains neither the current directory nor the user’s site-packages directory. All <code class="docutils literal notranslate">PYTHON*</code> environment variables are ignored, too. Many standard library modules contain code that is invoked on their execution as a script. An example is the <a class="reference internal" href="../library/timeit.html#module-timeit" title="timeit: Measure the execution time of small code snippets."><code class="xref py py-mod docutils literal notranslate">timeit</code></a> module: <div class="highlight-sh notranslate"><div class="highlight"><pre>python -m timeit -s "setup here" "benchmarked code here" python -m timeit -h # for details </pre></div> </div> Raises an <a class="reference internal" href="../library/sys.html#auditing">auditing event</a> <code class="docutils literal notranslate">cpython.run_module</code> with argument <code class="docutils literal notranslate">module-name</code>. <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="reference internal" href="../library/runpy.html#runpy.run_module" title="runpy.run_module"><code class="xref py py-func docutils literal notranslate">runpy.run_module()</code></a></dt><dd>Equivalent functionality directly available to Python code </dd> </dl> <a class="pep reference external" href="https://peps.python.org/pep-0338/">PEP 338</a> – Executing modules as scripts </div> <div class="versionchanged"> Changed in version 3.1: Supply the package name to run a <code class="docutils literal notranslate">__main__</code> submodule. </div> <div class="versionchanged"> Changed in version 3.4: namespace packages are also supported </div> </dd></dl> <dl class="describe" id="cmdarg-dash"> <dt class="sig sig-object"> -</dt> <dd>Read commands from standard input (<a class="reference internal" href="../library/sys.html#sys.stdin" title="sys.stdin"><code class="xref py py-data docutils literal notranslate">sys.stdin</code></a>). If standard input is a terminal, <a class="reference internal" href="#cmdoption-i"><code class="xref std std-option docutils literal notranslate">-i</code></a> is implied. If this option is given, the first element of <a class="reference internal" href="../library/sys.html#sys.argv" title="sys.argv"><code class="xref py py-data docutils literal notranslate">sys.argv</code></a> will be <code class="docutils literal notranslate">"-"</code> and the current directory will be added to the start of <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a>. Raises an <a class="reference internal" href="../library/sys.html#auditing">auditing event</a> <code class="docutils literal notranslate">cpython.run_stdin</code> with no arguments. </dd></dl> <dl class="describe" id="cmdarg-script"> <dt class="sig sig-object"> <script></dt> <dd>Execute the Python code contained in script, which must be a filesystem path (absolute or relative) referring to either a Python file, a directory containing a <code class="docutils literal notranslate">__main__.py</code> file, or a zipfile containing a <code class="docutils literal notranslate">__main__.py</code> file. If this option is given, the first element of <a class="reference internal" href="../library/sys.html#sys.argv" title="sys.argv"><code class="xref py py-data docutils literal notranslate">sys.argv</code></a> will be the script name as given on the command line. If the script name refers directly to a Python file, the directory containing that file is added to the start of <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a>, and the file is executed as the <a class="reference internal" href="../library/__main__.html#module-__main__" title="__main__: The environment where top-level code is run. Covers command-line interfaces, import-time behavior, and ``__name__ == '__main__'``."><code class="xref py py-mod docutils literal notranslate">__main__</code></a> module. If the script name refers to a directory or zipfile, the script name is added to the start of <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a> and the <code class="docutils literal notranslate">__main__.py</code> file in that location is executed as the <a class="reference internal" href="../library/__main__.html#module-__main__" title="__main__: The environment where top-level code is run. Covers command-line interfaces, import-time behavior, and ``__name__ == '__main__'``."><code class="xref py py-mod docutils literal notranslate">__main__</code></a> module. <a class="reference internal" href="#cmdoption-I"><code class="xref std std-option docutils literal notranslate">-I</code></a> option can be used to run the script in isolated mode where <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a> contains neither the script’s directory nor the user’s site-packages directory. All <code class="docutils literal notranslate">PYTHON*</code> environment variables are ignored, too. Raises an <a class="reference internal" href="../library/sys.html#auditing">auditing event</a> <code class="docutils literal notranslate">cpython.run_file</code> with argument <code class="docutils literal notranslate">filename</code>. <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="reference internal" href="../library/runpy.html#runpy.run_path" title="runpy.run_path"><code class="xref py py-func docutils literal notranslate">runpy.run_path()</code></a></dt><dd>Equivalent functionality directly available to Python code </dd> </dl> </div> </dd></dl> If no interface option is given, <a class="reference internal" href="#cmdoption-i"><code class="xref std std-option docutils literal notranslate">-i</code></a> is implied, <code class="docutils literal notranslate">sys.argv[0]</code> is an empty string (<code class="docutils literal notranslate">""</code>) and the current directory will be added to the start of <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a>. Also, tab-completion and history editing is automatically enabled, if available on your platform (see <a class="reference internal" href="../library/site.html#rlcompleter-config">Readline configuration</a>). <div class="admonition seealso"> See also <a class="reference internal" href="../tutorial/interpreter.html#tut-invoking">Invoking the Interpreter</a> </div> <div class="versionchanged"> Changed in version 3.4: Automatic enabling of tab-completion and history editing. </div> </section> <section id="generic-options"> <h3>1.1.2. Generic options<a class="headerlink" href="#generic-options" title="Link to this heading">¶</a></h3> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-0"> -?<a class="headerlink" href="#cmdoption-0" title="Link to this definition">¶</a></dt> <dt class="sig sig-object std" id="cmdoption-h"> -h<a class="headerlink" href="#cmdoption-h" title="Link to this definition">¶</a></dt> <dt class="sig sig-object std" id="cmdoption-help"> --help<a class="headerlink" href="#cmdoption-help" title="Link to this definition">¶</a></dt> <dd>Print a short description of all command line options and corresponding environment variables and exit. </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-help-env"> --help-env<a class="headerlink" href="#cmdoption-help-env" title="Link to this definition">¶</a></dt> <dd>Print a short description of Python-specific environment variables and exit. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-help-xoptions"> --help-xoptions<a class="headerlink" href="#cmdoption-help-xoptions" title="Link to this definition">¶</a></dt> <dd>Print a description of implementation-specific <a class="reference internal" href="#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X</code></a> options and exit. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-help-all"> --help-all<a class="headerlink" href="#cmdoption-help-all" title="Link to this definition">¶</a></dt> <dd>Print complete usage information and exit. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-V"> -V<a class="headerlink" href="#cmdoption-V" title="Link to this definition">¶</a></dt> <dt class="sig sig-object std" id="cmdoption-version"> --version<a class="headerlink" href="#cmdoption-version" title="Link to this definition">¶</a></dt> <dd>Print the Python version number and exit. Example output could be: <div class="highlight-none notranslate"><div class="highlight"><pre>Python 3.8.0b2+ </pre></div> </div> When given twice, print more information about the build, like: <div class="highlight-none notranslate"><div class="highlight"><pre>Python 3.8.0b2+ (3.8:0c076caaa8, Apr 20 2019, 21:55:00) [GCC 6.2.0 20161005] </pre></div> </div> <div class="versionadded"> Added in version 3.6: The <code class="docutils literal notranslate">-VV</code> option. </div> </dd></dl> </section> <section id="miscellaneous-options"> <h3>1.1.3. Miscellaneous options<a class="headerlink" href="#miscellaneous-options" title="Link to this heading">¶</a></h3> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-b"> -b<a class="headerlink" href="#cmdoption-b" title="Link to this definition">¶</a></dt> <dd>Issue a warning when converting <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a> or <a class="reference internal" href="../library/stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate">bytearray</code></a> to <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a> without specifying encoding or comparing <code class="xref py py-class docutils literal notranslate">bytes</code> or <code class="xref py py-class docutils literal notranslate">bytearray</code> with <code class="xref py py-class docutils literal notranslate">str</code> or <code class="xref py py-class docutils literal notranslate">bytes</code> with <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a>. Issue an error when the option is given twice (<code class="xref std std-option docutils literal notranslate">-bb</code>). <div class="versionchanged"> Changed in version 3.5: Affects also comparisons of <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a> with <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a>. </div> </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-B"> -B<a class="headerlink" href="#cmdoption-B" title="Link to this definition">¶</a></dt> <dd>If given, Python won’t try to write <code class="docutils literal notranslate">.pyc</code> files on the import of source modules. See also <a class="reference internal" href="#envvar-PYTHONDONTWRITEBYTECODE"><code class="xref std std-envvar docutils literal notranslate">PYTHONDONTWRITEBYTECODE</code></a>. </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-check-hash-based-pycs"> --check-hash-based-pycs default|always|never<a class="headerlink" href="#cmdoption-check-hash-based-pycs" title="Link to this definition">¶</a></dt> <dd>Control the validation behavior of hash-based <code class="docutils literal notranslate">.pyc</code> files. See <a class="reference internal" href="../reference/import.html#pyc-invalidation">Cached bytecode invalidation</a>. When set to <code class="docutils literal notranslate">default</code>, checked and unchecked hash-based bytecode cache files are validated according to their default semantics. When set to <code class="docutils literal notranslate">always</code>, all hash-based <code class="docutils literal notranslate">.pyc</code> files, whether checked or unchecked, are validated against their corresponding source file. When set to <code class="docutils literal notranslate">never</code>, hash-based <code class="docutils literal notranslate">.pyc</code> files are not validated against their corresponding source files. The semantics of timestamp-based <code class="docutils literal notranslate">.pyc</code> files are unaffected by this option. </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-d"> -d<a class="headerlink" href="#cmdoption-d" title="Link to this definition">¶</a></dt> <dd>Turn on parser debugging output (for expert only). See also the <a class="reference internal" href="#envvar-PYTHONDEBUG"><code class="xref std std-envvar docutils literal notranslate">PYTHONDEBUG</code></a> environment variable. This option requires a <a class="reference internal" href="configure.html#debug-build">debug build of Python</a>, otherwise it’s ignored. </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-E"> -E<a class="headerlink" href="#cmdoption-E" title="Link to this definition">¶</a></dt> <dd>Ignore all <code class="docutils literal notranslate">PYTHON*</code> environment variables, e.g. <a class="reference internal" href="#envvar-PYTHONPATH"><code class="xref std std-envvar docutils literal notranslate">PYTHONPATH</code></a> and <a class="reference internal" href="#envvar-PYTHONHOME"><code class="xref std std-envvar docutils literal notranslate">PYTHONHOME</code></a>, that might be set. See also the <a class="reference internal" href="#cmdoption-P"><code class="xref std std-option docutils literal notranslate">-P</code></a> and <a class="reference internal" href="#cmdoption-I"><code class="xref std std-option docutils literal notranslate">-I</code></a> (isolated) options. </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-i"> -i<a class="headerlink" href="#cmdoption-i" title="Link to this definition">¶</a></dt> <dd>When a script is passed as first argument or the <a class="reference internal" href="#cmdoption-c"><code class="xref std std-option docutils literal notranslate">-c</code></a> option is used, enter interactive mode after executing the script or the command, even when <a class="reference internal" href="../library/sys.html#sys.stdin" title="sys.stdin"><code class="xref py py-data docutils literal notranslate">sys.stdin</code></a> does not appear to be a terminal. The <a class="reference internal" href="#envvar-PYTHONSTARTUP"><code class="xref std std-envvar docutils literal notranslate">PYTHONSTARTUP</code></a> file is not read. This can be useful to inspect global variables or a stack trace when a script raises an exception. See also <a class="reference internal" href="#envvar-PYTHONINSPECT"><code class="xref std std-envvar docutils literal notranslate">PYTHONINSPECT</code></a>. </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-I"> -I<a class="headerlink" href="#cmdoption-I" title="Link to this definition">¶</a></dt> <dd>Run Python in isolated mode. This also implies <a class="reference internal" href="#cmdoption-E"><code class="xref std std-option docutils literal notranslate">-E</code></a>, <a class="reference internal" href="#cmdoption-P"><code class="xref std std-option docutils literal notranslate">-P</code></a> and <a class="reference internal" href="#cmdoption-s"><code class="xref std std-option docutils literal notranslate">-s</code></a> options. In isolated mode <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a> contains neither the script’s directory nor the user’s site-packages directory. All <code class="docutils literal notranslate">PYTHON*</code> environment variables are ignored, too. Further restrictions may be imposed to prevent the user from injecting malicious code. <div class="versionadded"> Added in version 3.4. </div> </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-O"> -O<a class="headerlink" href="#cmdoption-O" title="Link to this definition">¶</a></dt> <dd>Remove assert statements and any code conditional on the value of <a class="reference internal" href="../library/constants.html#debug__" title="__debug__"><code class="xref py py-const docutils literal notranslate">__debug__</code></a>. Augment the filename for compiled (<a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a>) files by adding <code class="docutils literal notranslate">.opt-1</code> before the <code class="docutils literal notranslate">.pyc</code> extension (see <a class="pep reference external" href="https://peps.python.org/pep-0488/">PEP 488</a>). See also <a class="reference internal" href="#envvar-PYTHONOPTIMIZE"><code class="xref std std-envvar docutils literal notranslate">PYTHONOPTIMIZE</code></a>. <div class="versionchanged"> Changed in version 3.5: Modify <code class="docutils literal notranslate">.pyc</code> filenames according to <a class="pep reference external" href="https://peps.python.org/pep-0488/">PEP 488</a>. </div> </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-OO"> -OO<a class="headerlink" href="#cmdoption-OO" title="Link to this definition">¶</a></dt> <dd>Do <a class="reference internal" href="#cmdoption-O"><code class="xref std std-option docutils literal notranslate">-O</code></a> and also discard docstrings. Augment the filename for compiled (<a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a>) files by adding <code class="docutils literal notranslate">.opt-2</code> before the <code class="docutils literal notranslate">.pyc</code> extension (see <a class="pep reference external" href="https://peps.python.org/pep-0488/">PEP 488</a>). <div class="versionchanged"> Changed in version 3.5: Modify <code class="docutils literal notranslate">.pyc</code> filenames according to <a class="pep reference external" href="https://peps.python.org/pep-0488/">PEP 488</a>. </div> </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-P"> -P<a class="headerlink" href="#cmdoption-P" title="Link to this definition">¶</a></dt> <dd>Don’t prepend a potentially unsafe path to <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a>: <ul class="simple"> <li><code class="docutils literal notranslate">python -m module</code> command line: Don’t prepend the current working directory.</li> <li><code class="docutils literal notranslate">python script.py</code> command line: Don’t prepend the script’s directory. If it’s a symbolic link, resolve symbolic links.</li> <li><code class="docutils literal notranslate">python -c code</code> and <code class="docutils literal notranslate">python</code> (REPL) command lines: Don’t prepend an empty string, which means the current working directory.</li> </ul> See also the <a class="reference internal" href="#envvar-PYTHONSAFEPATH"><code class="xref std std-envvar docutils literal notranslate">PYTHONSAFEPATH</code></a> environment variable, and <a class="reference internal" href="#cmdoption-E"><code class="xref std std-option docutils literal notranslate">-E</code></a> and <a class="reference internal" href="#cmdoption-I"><code class="xref std std-option docutils literal notranslate">-I</code></a> (isolated) options. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-q"> -q<a class="headerlink" href="#cmdoption-q" title="Link to this definition">¶</a></dt> <dd>Don’t display the copyright and version messages even in interactive mode. <div class="versionadded"> Added in version 3.2. </div> </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-R"> -R<a class="headerlink" href="#cmdoption-R" title="Link to this definition">¶</a></dt> <dd>Turn on hash randomization. This option only has an effect if the <a class="reference internal" href="#envvar-PYTHONHASHSEED"><code class="xref std std-envvar docutils literal notranslate">PYTHONHASHSEED</code></a> environment variable is set to <code class="docutils literal notranslate">0</code>, since hash randomization is enabled by default. On previous versions of Python, this option turns on hash randomization, so that the <a class="reference internal" href="../reference/datamodel.html#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> values of str and bytes objects are “salted” with an unpredictable random value. Although they remain constant within an individual Python process, they are not predictable between repeated invocations of Python. Hash randomization is intended to provide protection against a denial-of-service caused by carefully chosen inputs that exploit the worst case performance of a dict construction, O(n2) complexity. See <a class="reference external" href="http://ocert.org/advisories/ocert-2011-003.html">http://ocert.org/advisories/ocert-2011-003.html</a> for details. <a class="reference internal" href="#envvar-PYTHONHASHSEED"><code class="xref std std-envvar docutils literal notranslate">PYTHONHASHSEED</code></a> allows you to set a fixed value for the hash seed secret. <div class="versionadded"> Added in version 3.2.3. </div> <div class="versionchanged"> Changed in version 3.7: The option is no longer ignored. </div> </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-s"> -s<a class="headerlink" href="#cmdoption-s" title="Link to this definition">¶</a></dt> <dd>Don’t add the <a class="reference internal" href="../library/site.html#site.USER_SITE" title="site.USER_SITE"><code class="xref py py-data docutils literal notranslate">user site-packages directory</code></a> to <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a>. See also <a class="reference internal" href="#envvar-PYTHONNOUSERSITE"><code class="xref std std-envvar docutils literal notranslate">PYTHONNOUSERSITE</code></a>. <div class="admonition seealso"> See also <a class="pep reference external" href="https://peps.python.org/pep-0370/">PEP 370</a> – Per user site-packages directory </div> </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-S"> -S<a class="headerlink" href="#cmdoption-S" title="Link to this definition">¶</a></dt> <dd>Disable the import of the module <a class="reference internal" href="../library/site.html#module-site" title="site: Module responsible for site-specific configuration."><code class="xref py py-mod docutils literal notranslate">site</code></a> and the site-dependent manipulations of <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a> that it entails. Also disable these manipulations if <a class="reference internal" href="../library/site.html#module-site" title="site: Module responsible for site-specific configuration."><code class="xref py py-mod docutils literal notranslate">site</code></a> is explicitly imported later (call <a class="reference internal" href="../library/site.html#site.main" title="site.main"><code class="xref py py-func docutils literal notranslate">site.main()</code></a> if you want them to be triggered). </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-u"> -u<a class="headerlink" href="#cmdoption-u" title="Link to this definition">¶</a></dt> <dd>Force the stdout and stderr streams to be unbuffered. This option has no effect on the stdin stream. See also <a class="reference internal" href="#envvar-PYTHONUNBUFFERED"><code class="xref std std-envvar docutils literal notranslate">PYTHONUNBUFFERED</code></a>. <div class="versionchanged"> Changed in version 3.7: The text layer of the stdout and stderr streams now is unbuffered. </div> </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-v"> -v<a class="headerlink" href="#cmdoption-v" title="Link to this definition">¶</a></dt> <dd>Print a message each time a module is initialized, showing the place (filename or built-in module) from which it is loaded. When given twice (<code class="xref std std-option docutils literal notranslate">-vv</code>), print a message for each file that is checked for when searching for a module. Also provides information on module cleanup at exit. <div class="versionchanged"> Changed in version 3.10: The <a class="reference internal" href="../library/site.html#module-site" title="site: Module responsible for site-specific configuration."><code class="xref py py-mod docutils literal notranslate">site</code></a> module reports the site-specific paths and <code class="file docutils literal notranslate">.pth</code> files being processed. </div> See also <a class="reference internal" href="#envvar-PYTHONVERBOSE"><code class="xref std std-envvar docutils literal notranslate">PYTHONVERBOSE</code></a>. </dd></dl> <dl class="std option" id="using-on-warnings"> <dt class="sig sig-object std" id="cmdoption-W"> -W arg<a class="headerlink" href="#cmdoption-W" title="Link to this definition">¶</a></dt> <dd>Warning control. Python’s warning machinery by default prints warning messages to <a class="reference internal" href="../library/sys.html#sys.stderr" title="sys.stderr"><code class="xref py py-data docutils literal notranslate">sys.stderr</code></a>. The simplest settings apply a particular action unconditionally to all warnings emitted by a process (even those that are otherwise ignored by default): <div class="highlight-sh notranslate"><div class="highlight"><pre>-Wdefault # Warn once per call location -Werror # Convert to exceptions -Walways # Warn every time -Wall # Same as -Walways -Wmodule # Warn once per calling module -Wonce # Warn once per Python process -Wignore # Never warn </pre></div> </div> The action names can be abbreviated as desired and the interpreter will resolve them to the appropriate action name. For example, <code class="docutils literal notranslate">-Wi</code> is the same as <code class="docutils literal notranslate">-Wignore</code>. The full form of argument is: <div class="highlight-sh notranslate"><div class="highlight"><pre>action:message:category:module:lineno </pre></div> </div> Empty fields match all values; trailing empty fields may be omitted. For example <code class="docutils literal notranslate">-W ignore::DeprecationWarning</code> ignores all DeprecationWarning warnings. The action field is as explained above but only applies to warnings that match the remaining fields. The message field must match the whole warning message; this match is case-insensitive. The category field matches the warning category (ex: <code class="docutils literal notranslate">DeprecationWarning</code>). This must be a class name; the match test whether the actual warning category of the message is a subclass of the specified warning category. The module field matches the (fully qualified) module name; this match is case-sensitive. The lineno field matches the line number, where zero matches all line numbers and is thus equivalent to an omitted line number. Multiple <a class="reference internal" href="#cmdoption-W"><code class="xref std std-option docutils literal notranslate">-W</code></a> options can be given; when a warning matches more than one option, the action for the last matching option is performed. Invalid <a class="reference internal" href="#cmdoption-W"><code class="xref std std-option docutils literal notranslate">-W</code></a> options are ignored (though, a warning message is printed about invalid options when the first warning is issued). Warnings can also be controlled using the <a class="reference internal" href="#envvar-PYTHONWARNINGS"><code class="xref std std-envvar docutils literal notranslate">PYTHONWARNINGS</code></a> environment variable and from within a Python program using the <a class="reference internal" href="../library/warnings.html#module-warnings" title="warnings: Issue warning messages and control their disposition."><code class="xref py py-mod docutils literal notranslate">warnings</code></a> module. For example, the <a class="reference internal" href="../library/warnings.html#warnings.filterwarnings" title="warnings.filterwarnings"><code class="xref py py-func docutils literal notranslate">warnings.filterwarnings()</code></a> function can be used to use a regular expression on the warning message. See <a class="reference internal" href="../library/warnings.html#warning-filter">The Warnings Filter</a> and <a class="reference internal" href="../library/warnings.html#describing-warning-filters">Describing Warning Filters</a> for more details. </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-x"> -x<a class="headerlink" href="#cmdoption-x" title="Link to this definition">¶</a></dt> <dd>Skip the first line of the source, allowing use of non-Unix forms of <code class="docutils literal notranslate">#!cmd</code>. This is intended for a DOS specific hack only. </dd></dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-X"> -X<a class="headerlink" href="#cmdoption-X" title="Link to this definition">¶</a></dt> <dd>Reserved for various implementation-specific options. CPython currently defines the following possible values: <ul> <li><code class="docutils literal notranslate">-X faulthandler</code> to enable <a class="reference internal" href="../library/faulthandler.html#module-faulthandler" title="faulthandler: Dump the Python traceback."><code class="xref py py-mod docutils literal notranslate">faulthandler</code></a>. See also <a class="reference internal" href="#envvar-PYTHONFAULTHANDLER"><code class="xref std std-envvar docutils literal notranslate">PYTHONFAULTHANDLER</code></a>. <div class="versionadded"> Added in version 3.3. </div> </li> <li><code class="docutils literal notranslate">-X showrefcount</code> to output the total reference count and number of used memory blocks when the program finishes or after each statement in the interactive interpreter. This only works on <a class="reference internal" href="configure.html#debug-build">debug builds</a>. <div class="versionadded"> Added in version 3.4. </div> </li> <li><code class="docutils literal notranslate">-X tracemalloc</code> to start tracing Python memory allocations using the <a class="reference internal" href="../library/tracemalloc.html#module-tracemalloc" title="tracemalloc: Trace memory allocations."><code class="xref py py-mod docutils literal notranslate">tracemalloc</code></a> module. By default, only the most recent frame is stored in a traceback of a trace. Use <code class="docutils literal notranslate">-X tracemalloc=NFRAME</code> to start tracing with a traceback limit of NFRAME frames. See <a class="reference internal" href="../library/tracemalloc.html#tracemalloc.start" title="tracemalloc.start"><code class="xref py py-func docutils literal notranslate">tracemalloc.start()</code></a> and <a class="reference internal" href="#envvar-PYTHONTRACEMALLOC"><code class="xref std std-envvar docutils literal notranslate">PYTHONTRACEMALLOC</code></a> for more information. <div class="versionadded"> Added in version 3.4. </div> </li> <li><code class="docutils literal notranslate">-X int_max_str_digits</code> configures the <a class="reference internal" href="../library/stdtypes.html#int-max-str-digits">integer string conversion length limitation</a>. See also <a class="reference internal" href="#envvar-PYTHONINTMAXSTRDIGITS"><code class="xref std std-envvar docutils literal notranslate">PYTHONINTMAXSTRDIGITS</code></a>. <div class="versionadded"> Added in version 3.11. </div> </li> <li><code class="docutils literal notranslate">-X importtime</code> to show how long each import takes. It shows module name, cumulative time (including nested imports) and self time (excluding nested imports). Note that its output may be broken in multi-threaded application. Typical usage is <code class="docutils literal notranslate">python3 -X importtime -c 'import asyncio'</code>. See also <a class="reference internal" href="#envvar-PYTHONPROFILEIMPORTTIME"><code class="xref std std-envvar docutils literal notranslate">PYTHONPROFILEIMPORTTIME</code></a>. <div class="versionadded"> Added in version 3.7. </div> </li> <li><code class="docutils literal notranslate">-X dev</code>: enable <a class="reference internal" href="../library/devmode.html#devmode">Python Development Mode</a>, introducing additional runtime checks that are too expensive to be enabled by default. See also <a class="reference internal" href="#envvar-PYTHONDEVMODE"><code class="xref std std-envvar docutils literal notranslate">PYTHONDEVMODE</code></a>. <div class="versionadded"> Added in version 3.7. </div> </li> <li><code class="docutils literal notranslate">-X utf8</code> enables the <a class="reference internal" href="../library/os.html#utf8-mode">Python UTF-8 Mode</a>. <code class="docutils literal notranslate">-X utf8=0</code> explicitly disables <a class="reference internal" href="../library/os.html#utf8-mode">Python UTF-8 Mode</a> (even when it would otherwise activate automatically). See also <a class="reference internal" href="#envvar-PYTHONUTF8"><code class="xref std std-envvar docutils literal notranslate">PYTHONUTF8</code></a>. <div class="versionadded"> Added in version 3.7. </div> </li> <li><code class="docutils literal notranslate">-X pycache_prefix=PATH</code> enables writing <code class="docutils literal notranslate">.pyc</code> files to a parallel tree rooted at the given directory instead of to the code tree. See also <a class="reference internal" href="#envvar-PYTHONPYCACHEPREFIX"><code class="xref std std-envvar docutils literal notranslate">PYTHONPYCACHEPREFIX</code></a>. <div class="versionadded"> Added in version 3.8. </div> </li> <li><code class="docutils literal notranslate">-X warn_default_encoding</code> issues a <a class="reference internal" href="../library/exceptions.html#EncodingWarning" title="EncodingWarning"><code class="xref py py-class docutils literal notranslate">EncodingWarning</code></a> when the locale-specific default encoding is used for opening files. See also <a class="reference internal" href="#envvar-PYTHONWARNDEFAULTENCODING"><code class="xref std std-envvar docutils literal notranslate">PYTHONWARNDEFAULTENCODING</code></a>. <div class="versionadded"> Added in version 3.10. </div> </li> <li><code class="docutils literal notranslate">-X no_debug_ranges</code> disables the inclusion of the tables mapping extra location information (end line, start column offset and end column offset) to every instruction in code objects. This is useful when smaller code objects and pyc files are desired as well as suppressing the extra visual location indicators when the interpreter displays tracebacks. See also <a class="reference internal" href="#envvar-PYTHONNODEBUGRANGES"><code class="xref std std-envvar docutils literal notranslate">PYTHONNODEBUGRANGES</code></a>. <div class="versionadded"> Added in version 3.11. </div> </li> <li><code class="docutils literal notranslate">-X frozen_modules</code> determines whether or not frozen modules are ignored by the import machinery. A value of <code class="docutils literal notranslate">on</code> means they get imported and <code class="docutils literal notranslate">off</code> means they are ignored. The default is <code class="docutils literal notranslate">on</code> if this is an installed Python (the normal case). If it’s under development (running from the source tree) then the default is <code class="docutils literal notranslate">off</code>. Note that the <code class="xref py py-mod docutils literal notranslate">importlib_bootstrap</code> and <code class="xref py py-mod docutils literal notranslate">importlib_bootstrap_external</code> frozen modules are always used, even if this flag is set to <code class="docutils literal notranslate">off</code>. See also <a class="reference internal" href="#envvar-PYTHON_FROZEN_MODULES"><code class="xref std std-envvar docutils literal notranslate">PYTHON_FROZEN_MODULES</code></a>. <div class="versionadded"> Added in version 3.11. </div> </li> <li><code class="docutils literal notranslate">-X perf</code> enables support for the Linux <code class="docutils literal notranslate">perf</code> profiler. When this option is provided, the <code class="docutils literal notranslate">perf</code> profiler will be able to report Python calls. This option is only available on some platforms and will do nothing if is not supported on the current system. The default value is “off”. See also <a class="reference internal" href="#envvar-PYTHONPERFSUPPORT"><code class="xref std std-envvar docutils literal notranslate">PYTHONPERFSUPPORT</code></a> and <a class="reference internal" href="../howto/perf_profiling.html#perf-profiling">Python support for the Linux perf profiler</a>. <div class="versionadded"> Added in version 3.12. </div> </li> <li><code class="docutils literal notranslate">-X perf_jit</code> enables support for the Linux <code class="docutils literal notranslate">perf</code> profiler with DWARF support. When this option is provided, the <code class="docutils literal notranslate">perf</code> profiler will be able to report Python calls using DWARF information. This option is only available on some platforms and will do nothing if is not supported on the current system. The default value is “off”. See also <a class="reference internal" href="#envvar-PYTHON_PERF_JIT_SUPPORT"><code class="xref std std-envvar docutils literal notranslate">PYTHON_PERF_JIT_SUPPORT</code></a> and <a class="reference internal" href="../howto/perf_profiling.html#perf-profiling">Python support for the Linux perf profiler</a>. <div class="versionadded"> Added in version 3.13. </div> </li> <li><code class="samp docutils literal notranslate">-X cpu_count=n</code> overrides <a class="reference internal" href="../library/os.html#os.cpu_count" title="os.cpu_count"><code class="xref py py-func docutils literal notranslate">os.cpu_count()</code></a>, <a class="reference internal" href="../library/os.html#os.process_cpu_count" title="os.process_cpu_count"><code class="xref py py-func docutils literal notranslate">os.process_cpu_count()</code></a>, and <a class="reference internal" href="../library/multiprocessing.html#multiprocessing.cpu_count" title="multiprocessing.cpu_count"><code class="xref py py-func docutils literal notranslate">multiprocessing.cpu_count()</code></a>. n must be greater than or equal to 1. This option may be useful for users who need to limit CPU resources of a container system. See also <a class="reference internal" href="#envvar-PYTHON_CPU_COUNT"><code class="xref std std-envvar docutils literal notranslate">PYTHON_CPU_COUNT</code></a>. If n is <code class="docutils literal notranslate">default</code>, nothing is overridden. <div class="versionadded"> Added in version 3.13. </div> </li> <li><code class="samp docutils literal notranslate">-X presite=package.module</code> specifies a module that should be imported before the <a class="reference internal" href="../library/site.html#module-site" title="site: Module responsible for site-specific configuration."><code class="xref py py-mod docutils literal notranslate">site</code></a> module is executed and before the <a class="reference internal" href="../library/__main__.html#module-__main__" title="__main__: The environment where top-level code is run. Covers command-line interfaces, import-time behavior, and ``__name__ == '__main__'``."><code class="xref py py-mod docutils literal notranslate">__main__</code></a> module exists. Therefore, the imported module isn’t <a class="reference internal" href="../library/__main__.html#module-__main__" title="__main__: The environment where top-level code is run. Covers command-line interfaces, import-time behavior, and ``__name__ == '__main__'``."><code class="xref py py-mod docutils literal notranslate">__main__</code></a>. This can be used to execute code early during Python initialization. Python needs to be <a class="reference internal" href="configure.html#debug-build">built in debug mode</a> for this option to exist. See also <a class="reference internal" href="#envvar-PYTHON_PRESITE"><code class="xref std std-envvar docutils literal notranslate">PYTHON_PRESITE</code></a>. <div class="versionadded"> Added in version 3.13. </div> </li> <li><code class="samp docutils literal notranslate">-X gil=0,1</code> forces the GIL to be disabled or enabled, respectively. Setting to <code class="docutils literal notranslate">0</code> is only available in builds configured with <a class="reference internal" href="configure.html#cmdoption-disable-gil"><code class="xref std std-option docutils literal notranslate">--disable-gil</code></a>. See also <a class="reference internal" href="#envvar-PYTHON_GIL"><code class="xref std std-envvar docutils literal notranslate">PYTHON_GIL</code></a> and <a class="reference internal" href="../whatsnew/3.13.html#whatsnew313-free-threaded-cpython">Free-threaded CPython</a>. <div class="versionadded"> Added in version 3.13. </div> </li> </ul> It also allows passing arbitrary values and retrieving them through the <a class="reference internal" href="../library/sys.html#sys._xoptions" title="sys._xoptions"><code class="xref py py-data docutils literal notranslate">sys._xoptions</code></a> dictionary. <div class="versionadded"> Added in version 3.2. </div> <div class="versionchanged"> Changed in version 3.9: Removed the <code class="docutils literal notranslate">-X showalloccount</code> option. </div> <div class="versionchanged"> Changed in version 3.10: Removed the <code class="docutils literal notranslate">-X oldparser</code> option. </div> </dd></dl> </section> <section id="controlling-color"> <h3>1.1.4. Controlling color<a class="headerlink" href="#controlling-color" title="Link to this heading">¶</a></h3> The Python interpreter is configured by default to use colors to highlight output in certain situations such as when displaying tracebacks. This behavior can be controlled by setting different environment variables. Setting the environment variable <code class="docutils literal notranslate">TERM</code> to <code class="docutils literal notranslate">dumb</code> will disable color. If the <a class="reference external" href="https://force-color.org/"><code class="docutils literal notranslate">FORCE_COLOR</code></a> environment variable is set, then color will be enabled regardless of the value of TERM. This is useful on CI systems which aren’t terminals but can still display ANSI escape sequences. If the <a class="reference external" href="https://no-color.org/"><code class="docutils literal notranslate">NO_COLOR</code></a> environment variable is set, Python will disable all color in the output. This takes precedence over <code class="docutils literal notranslate">FORCE_COLOR</code>. All these environment variables are used also by other tools to control color output. To control the color output only in the Python interpreter, the <a class="reference internal" href="#envvar-PYTHON_COLORS"><code class="xref std std-envvar docutils literal notranslate">PYTHON_COLORS</code></a> environment variable can be used. This variable takes precedence over <code class="docutils literal notranslate">NO_COLOR</code>, which in turn takes precedence over <code class="docutils literal notranslate">FORCE_COLOR</code>. </section> <section id="options-you-shouldn-t-use"> <h3>1.1.5. Options you shouldn’t use<a class="headerlink" href="#options-you-shouldn-t-use" title="Link to this heading">¶</a></h3> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-J"> -J<a class="headerlink" href="#cmdoption-J" title="Link to this definition">¶</a></dt> <dd>Reserved for use by <a class="reference external" href="https://www.jython.org/">Jython</a>. </dd></dl> </section> </section> <section id="environment-variables"> <h2>1.2. Environment variables<a class="headerlink" href="#environment-variables" title="Link to this heading">¶</a></h2> These environment variables influence Python’s behavior, they are processed before the command-line switches other than -E or -I. It is customary that command-line switches override environmental variables where there is a conflict. <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONHOME"> PYTHONHOME<a class="headerlink" href="#envvar-PYTHONHOME" title="Link to this definition">¶</a></dt> <dd>Change the location of the standard Python libraries. By default, the libraries are searched in <code class="file docutils literal notranslate">prefix/lib/pythonversion</code> and <code class="file docutils literal notranslate">exec_prefix/lib/pythonversion</code>, where <code class="file docutils literal notranslate">prefix</code> and <code class="file docutils literal notranslate">exec_prefix</code> are installation-dependent directories, both defaulting to <code class="file docutils literal notranslate">/usr/local</code>. When <a class="reference internal" href="#envvar-PYTHONHOME"><code class="xref std std-envvar docutils literal notranslate">PYTHONHOME</code></a> is set to a single directory, its value replaces both <code class="file docutils literal notranslate">prefix</code> and <code class="file docutils literal notranslate">exec_prefix</code>. To specify different values for these, set <a class="reference internal" href="#envvar-PYTHONHOME"><code class="xref std std-envvar docutils literal notranslate">PYTHONHOME</code></a> to <code class="file docutils literal notranslate">prefix:exec_prefix</code>. </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONPATH"> PYTHONPATH<a class="headerlink" href="#envvar-PYTHONPATH" title="Link to this definition">¶</a></dt> <dd>Augment the default search path for module files. The format is the same as the shell’s <code class="xref std std-envvar docutils literal notranslate">PATH</code>: one or more directory pathnames separated by <a class="reference internal" href="../library/os.html#os.pathsep" title="os.pathsep"><code class="xref py py-data docutils literal notranslate">os.pathsep</code></a> (e.g. colons on Unix or semicolons on Windows). Non-existent directories are silently ignored. In addition to normal directories, individual <a class="reference internal" href="#envvar-PYTHONPATH"><code class="xref std std-envvar docutils literal notranslate">PYTHONPATH</code></a> entries may refer to zipfiles containing pure Python modules (in either source or compiled form). Extension modules cannot be imported from zipfiles. The default search path is installation dependent, but generally begins with <code class="file docutils literal notranslate">prefix/lib/pythonversion</code> (see <a class="reference internal" href="#envvar-PYTHONHOME"><code class="xref std std-envvar docutils literal notranslate">PYTHONHOME</code></a> above). It is always appended to <a class="reference internal" href="#envvar-PYTHONPATH"><code class="xref std std-envvar docutils literal notranslate">PYTHONPATH</code></a>. An additional directory will be inserted in the search path in front of <a class="reference internal" href="#envvar-PYTHONPATH"><code class="xref std std-envvar docutils literal notranslate">PYTHONPATH</code></a> as described above under <a class="reference internal" href="#using-on-interface-options">Interface options</a>. The search path can be manipulated from within a Python program as the variable <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a>. </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONSAFEPATH"> PYTHONSAFEPATH<a class="headerlink" href="#envvar-PYTHONSAFEPATH" title="Link to this definition">¶</a></dt> <dd>If this is set to a non-empty string, don’t prepend a potentially unsafe path to <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a>: see the <a class="reference internal" href="#cmdoption-P"><code class="xref std std-option docutils literal notranslate">-P</code></a> option for details. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONPLATLIBDIR"> PYTHONPLATLIBDIR<a class="headerlink" href="#envvar-PYTHONPLATLIBDIR" title="Link to this definition">¶</a></dt> <dd>If this is set to a non-empty string, it overrides the <a class="reference internal" href="../library/sys.html#sys.platlibdir" title="sys.platlibdir"><code class="xref py py-data docutils literal notranslate">sys.platlibdir</code></a> value. <div class="versionadded"> Added in version 3.9. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONSTARTUP"> PYTHONSTARTUP<a class="headerlink" href="#envvar-PYTHONSTARTUP" title="Link to this definition">¶</a></dt> <dd>If this is the name of a readable file, the Python commands in that file are executed before the first prompt is displayed in interactive mode. The file is executed in the same namespace where interactive commands are executed so that objects defined or imported in it can be used without qualification in the interactive session. You can also change the prompts <a class="reference internal" href="../library/sys.html#sys.ps1" title="sys.ps1"><code class="xref py py-data docutils literal notranslate">sys.ps1</code></a> and <a class="reference internal" href="../library/sys.html#sys.ps2" title="sys.ps2"><code class="xref py py-data docutils literal notranslate">sys.ps2</code></a> and the hook <a class="reference internal" href="../library/sys.html#sys.__interactivehook__" title="sys.__interactivehook__"><code class="xref py py-data docutils literal notranslate">sys.__interactivehook__</code></a> in this file. Raises an <a class="reference internal" href="../library/sys.html#auditing">auditing event</a> <code class="docutils literal notranslate">cpython.run_startup</code> with the filename as the argument when called on startup. </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONOPTIMIZE"> PYTHONOPTIMIZE<a class="headerlink" href="#envvar-PYTHONOPTIMIZE" title="Link to this definition">¶</a></dt> <dd>If this is set to a non-empty string it is equivalent to specifying the <a class="reference internal" href="#cmdoption-O"><code class="xref std std-option docutils literal notranslate">-O</code></a> option. If set to an integer, it is equivalent to specifying <a class="reference internal" href="#cmdoption-O"><code class="xref std std-option docutils literal notranslate">-O</code></a> multiple times. </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONBREAKPOINT"> PYTHONBREAKPOINT<a class="headerlink" href="#envvar-PYTHONBREAKPOINT" title="Link to this definition">¶</a></dt> <dd>If this is set, it names a callable using dotted-path notation. The module containing the callable will be imported and then the callable will be run by the default implementation of <a class="reference internal" href="../library/sys.html#sys.breakpointhook" title="sys.breakpointhook"><code class="xref py py-func docutils literal notranslate">sys.breakpointhook()</code></a> which itself is called by built-in <a class="reference internal" href="../library/functions.html#breakpoint" title="breakpoint"><code class="xref py py-func docutils literal notranslate">breakpoint()</code></a>. If not set, or set to the empty string, it is equivalent to the value “pdb.set_trace”. Setting this to the string “0” causes the default implementation of <a class="reference internal" href="../library/sys.html#sys.breakpointhook" title="sys.breakpointhook"><code class="xref py py-func docutils literal notranslate">sys.breakpointhook()</code></a> to do nothing but return immediately. <div class="versionadded"> Added in version 3.7. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONDEBUG"> PYTHONDEBUG<a class="headerlink" href="#envvar-PYTHONDEBUG" title="Link to this definition">¶</a></dt> <dd>If this is set to a non-empty string it is equivalent to specifying the <a class="reference internal" href="#cmdoption-d"><code class="xref std std-option docutils literal notranslate">-d</code></a> option. If set to an integer, it is equivalent to specifying <a class="reference internal" href="#cmdoption-d"><code class="xref std std-option docutils literal notranslate">-d</code></a> multiple times. This environment variable requires a <a class="reference internal" href="configure.html#debug-build">debug build of Python</a>, otherwise it’s ignored. </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONINSPECT"> PYTHONINSPECT<a class="headerlink" href="#envvar-PYTHONINSPECT" title="Link to this definition">¶</a></dt> <dd>If this is set to a non-empty string it is equivalent to specifying the <a class="reference internal" href="#cmdoption-i"><code class="xref std std-option docutils literal notranslate">-i</code></a> option. This variable can also be modified by Python code using <a class="reference internal" href="../library/os.html#os.environ" title="os.environ"><code class="xref py py-data docutils literal notranslate">os.environ</code></a> to force inspect mode on program termination. Raises an <a class="reference internal" href="../library/sys.html#auditing">auditing event</a> <code class="docutils literal notranslate">cpython.run_stdin</code> with no arguments. <div class="versionchanged"> Changed in version 3.12.5: (also 3.11.10, 3.10.15, 3.9.20, and 3.8.20) Emits audit events. </div> <div class="versionchanged"> Changed in version 3.13: Uses PyREPL if possible, in which case <a class="reference internal" href="#envvar-PYTHONSTARTUP"><code class="xref std std-envvar docutils literal notranslate">PYTHONSTARTUP</code></a> is also executed. Emits audit events. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONUNBUFFERED"> PYTHONUNBUFFERED<a class="headerlink" href="#envvar-PYTHONUNBUFFERED" title="Link to this definition">¶</a></dt> <dd>If this is set to a non-empty string it is equivalent to specifying the <a class="reference internal" href="#cmdoption-u"><code class="xref std std-option docutils literal notranslate">-u</code></a> option. </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONVERBOSE"> PYTHONVERBOSE<a class="headerlink" href="#envvar-PYTHONVERBOSE" title="Link to this definition">¶</a></dt> <dd>If this is set to a non-empty string it is equivalent to specifying the <a class="reference internal" href="#cmdoption-v"><code class="xref std std-option docutils literal notranslate">-v</code></a> option. If set to an integer, it is equivalent to specifying <a class="reference internal" href="#cmdoption-v"><code class="xref std std-option docutils literal notranslate">-v</code></a> multiple times. </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONCASEOK"> PYTHONCASEOK<a class="headerlink" href="#envvar-PYTHONCASEOK" title="Link to this definition">¶</a></dt> <dd>If this is set, Python ignores case in <a class="reference internal" href="../reference/simple_stmts.html#import"><code class="xref std std-keyword docutils literal notranslate">import</code></a> statements. This only works on Windows and macOS. </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONDONTWRITEBYTECODE"> PYTHONDONTWRITEBYTECODE<a class="headerlink" href="#envvar-PYTHONDONTWRITEBYTECODE" title="Link to this definition">¶</a></dt> <dd>If this is set to a non-empty string, Python won’t try to write <code class="docutils literal notranslate">.pyc</code> files on the import of source modules. This is equivalent to specifying the <a class="reference internal" href="#cmdoption-B"><code class="xref std std-option docutils literal notranslate">-B</code></a> option. </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONPYCACHEPREFIX"> PYTHONPYCACHEPREFIX<a class="headerlink" href="#envvar-PYTHONPYCACHEPREFIX" title="Link to this definition">¶</a></dt> <dd>If this is set, Python will write <code class="docutils literal notranslate">.pyc</code> files in a mirror directory tree at this path, instead of in <code class="docutils literal notranslate">__pycache__</code> directories within the source tree. This is equivalent to specifying the <a class="reference internal" href="#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X</code></a> <code class="docutils literal notranslate">pycache_prefix=PATH</code> option. <div class="versionadded"> Added in version 3.8. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONHASHSEED"> PYTHONHASHSEED<a class="headerlink" href="#envvar-PYTHONHASHSEED" title="Link to this definition">¶</a></dt> <dd>If this variable is not set or set to <code class="docutils literal notranslate">random</code>, a random value is used to seed the hashes of str and bytes objects. If <a class="reference internal" href="#envvar-PYTHONHASHSEED"><code class="xref std std-envvar docutils literal notranslate">PYTHONHASHSEED</code></a> is set to an integer value, it is used as a fixed seed for generating the hash() of the types covered by the hash randomization. Its purpose is to allow repeatable hashing, such as for selftests for the interpreter itself, or to allow a cluster of python processes to share hash values. The integer must be a decimal number in the range [0,4294967295]. Specifying the value 0 will disable hash randomization. <div class="versionadded"> Added in version 3.2.3. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONINTMAXSTRDIGITS"> PYTHONINTMAXSTRDIGITS<a class="headerlink" href="#envvar-PYTHONINTMAXSTRDIGITS" title="Link to this definition">¶</a></dt> <dd>If this variable is set to an integer, it is used to configure the interpreter’s global <a class="reference internal" href="../library/stdtypes.html#int-max-str-digits">integer string conversion length limitation</a>. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONIOENCODING"> PYTHONIOENCODING<a class="headerlink" href="#envvar-PYTHONIOENCODING" title="Link to this definition">¶</a></dt> <dd>If this is set before running the interpreter, it overrides the encoding used for stdin/stdout/stderr, in the syntax <code class="docutils literal notranslate">encodingname:errorhandler</code>. Both the <code class="docutils literal notranslate">encodingname</code> and the <code class="docutils literal notranslate">:errorhandler</code> parts are optional and have the same meaning as in <a class="reference internal" href="../library/stdtypes.html#str.encode" title="str.encode"><code class="xref py py-func docutils literal notranslate">str.encode()</code></a>. For stderr, the <code class="docutils literal notranslate">:errorhandler</code> part is ignored; the handler will always be <code class="docutils literal notranslate">'backslashreplace'</code>. <div class="versionchanged"> Changed in version 3.4: The <code class="docutils literal notranslate">encodingname</code> part is now optional. </div> <div class="versionchanged"> Changed in version 3.6: On Windows, the encoding specified by this variable is ignored for interactive console buffers unless <a class="reference internal" href="#envvar-PYTHONLEGACYWINDOWSSTDIO"><code class="xref std std-envvar docutils literal notranslate">PYTHONLEGACYWINDOWSSTDIO</code></a> is also specified. Files and pipes redirected through the standard streams are not affected. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONNOUSERSITE"> PYTHONNOUSERSITE<a class="headerlink" href="#envvar-PYTHONNOUSERSITE" title="Link to this definition">¶</a></dt> <dd>If this is set, Python won’t add the <a class="reference internal" href="../library/site.html#site.USER_SITE" title="site.USER_SITE"><code class="xref py py-data docutils literal notranslate">user site-packages directory</code></a> to <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a>. <div class="admonition seealso"> See also <a class="pep reference external" href="https://peps.python.org/pep-0370/">PEP 370</a> – Per user site-packages directory </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONUSERBASE"> PYTHONUSERBASE<a class="headerlink" href="#envvar-PYTHONUSERBASE" title="Link to this definition">¶</a></dt> <dd>Defines the <a class="reference internal" href="../library/site.html#site.USER_BASE" title="site.USER_BASE"><code class="xref py py-data docutils literal notranslate">user base directory</code></a>, which is used to compute the path of the <a class="reference internal" href="../library/site.html#site.USER_SITE" title="site.USER_SITE"><code class="xref py py-data docutils literal notranslate">user site-packages directory</code></a> and <a class="reference internal" href="../library/sysconfig.html#sysconfig-user-scheme">installation paths</a> for <code class="docutils literal notranslate">python -m pip install --user</code>. <div class="admonition seealso"> See also <a class="pep reference external" href="https://peps.python.org/pep-0370/">PEP 370</a> – Per user site-packages directory </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONEXECUTABLE"> PYTHONEXECUTABLE<a class="headerlink" href="#envvar-PYTHONEXECUTABLE" title="Link to this definition">¶</a></dt> <dd>If this environment variable is set, <code class="docutils literal notranslate">sys.argv[0]</code> will be set to its value instead of the value got through the C runtime. Only works on macOS. </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONWARNINGS"> PYTHONWARNINGS<a class="headerlink" href="#envvar-PYTHONWARNINGS" title="Link to this definition">¶</a></dt> <dd>This is equivalent to the <a class="reference internal" href="#cmdoption-W"><code class="xref std std-option docutils literal notranslate">-W</code></a> option. If set to a comma separated string, it is equivalent to specifying <a class="reference internal" href="#cmdoption-W"><code class="xref std std-option docutils literal notranslate">-W</code></a> multiple times, with filters later in the list taking precedence over those earlier in the list. The simplest settings apply a particular action unconditionally to all warnings emitted by a process (even those that are otherwise ignored by default): <div class="highlight-sh notranslate"><div class="highlight"><pre>PYTHONWARNINGS=default # Warn once per call location PYTHONWARNINGS=error # Convert to exceptions PYTHONWARNINGS=always # Warn every time PYTHONWARNINGS=all # Same as PYTHONWARNINGS=always PYTHONWARNINGS=module # Warn once per calling module PYTHONWARNINGS=once # Warn once per Python process PYTHONWARNINGS=ignore # Never warn </pre></div> </div> See <a class="reference internal" href="../library/warnings.html#warning-filter">The Warnings Filter</a> and <a class="reference internal" href="../library/warnings.html#describing-warning-filters">Describing Warning Filters</a> for more details. </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONFAULTHANDLER"> PYTHONFAULTHANDLER<a class="headerlink" href="#envvar-PYTHONFAULTHANDLER" title="Link to this definition">¶</a></dt> <dd>If this environment variable is set to a non-empty string, <a class="reference internal" href="../library/faulthandler.html#faulthandler.enable" title="faulthandler.enable"><code class="xref py py-func docutils literal notranslate">faulthandler.enable()</code></a> is called at startup: install a handler for <a class="reference internal" href="../library/signal.html#signal.SIGSEGV" title="signal.SIGSEGV"><code class="xref py py-const docutils literal notranslate">SIGSEGV</code></a>, <a class="reference internal" href="../library/signal.html#signal.SIGFPE" title="signal.SIGFPE"><code class="xref py py-const docutils literal notranslate">SIGFPE</code></a>, <a class="reference internal" href="../library/signal.html#signal.SIGABRT" title="signal.SIGABRT"><code class="xref py py-const docutils literal notranslate">SIGABRT</code></a>, <a class="reference internal" href="../library/signal.html#signal.SIGBUS" title="signal.SIGBUS"><code class="xref py py-const docutils literal notranslate">SIGBUS</code></a> and <a class="reference internal" href="../library/signal.html#signal.SIGILL" title="signal.SIGILL"><code class="xref py py-const docutils literal notranslate">SIGILL</code></a> signals to dump the Python traceback. This is equivalent to <a class="reference internal" href="#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X</code></a> <code class="docutils literal notranslate">faulthandler</code> option. <div class="versionadded"> Added in version 3.3. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONTRACEMALLOC"> PYTHONTRACEMALLOC<a class="headerlink" href="#envvar-PYTHONTRACEMALLOC" title="Link to this definition">¶</a></dt> <dd>If this environment variable is set to a non-empty string, start tracing Python memory allocations using the <a class="reference internal" href="../library/tracemalloc.html#module-tracemalloc" title="tracemalloc: Trace memory allocations."><code class="xref py py-mod docutils literal notranslate">tracemalloc</code></a> module. The value of the variable is the maximum number of frames stored in a traceback of a trace. For example, <code class="docutils literal notranslate">PYTHONTRACEMALLOC=1</code> stores only the most recent frame. See the <a class="reference internal" href="../library/tracemalloc.html#tracemalloc.start" title="tracemalloc.start"><code class="xref py py-func docutils literal notranslate">tracemalloc.start()</code></a> function for more information. This is equivalent to setting the <a class="reference internal" href="#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X</code></a> <code class="docutils literal notranslate">tracemalloc</code> option. <div class="versionadded"> Added in version 3.4. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONPROFILEIMPORTTIME"> PYTHONPROFILEIMPORTTIME<a class="headerlink" href="#envvar-PYTHONPROFILEIMPORTTIME" title="Link to this definition">¶</a></dt> <dd>If this environment variable is set to a non-empty string, Python will show how long each import takes. This is equivalent to setting the <a class="reference internal" href="#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X</code></a> <code class="docutils literal notranslate">importtime</code> option. <div class="versionadded"> Added in version 3.7. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONASYNCIODEBUG"> PYTHONASYNCIODEBUG<a class="headerlink" href="#envvar-PYTHONASYNCIODEBUG" title="Link to this definition">¶</a></dt> <dd>If this environment variable is set to a non-empty string, enable the <a class="reference internal" href="../library/asyncio-dev.html#asyncio-debug-mode">debug mode</a> of the <a class="reference internal" href="../library/asyncio.html#module-asyncio" title="asyncio: Asynchronous I/O."><code class="xref py py-mod docutils literal notranslate">asyncio</code></a> module. <div class="versionadded"> Added in version 3.4. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONMALLOC"> PYTHONMALLOC<a class="headerlink" href="#envvar-PYTHONMALLOC" title="Link to this definition">¶</a></dt> <dd>Set the Python memory allocators and/or install debug hooks. Set the family of memory allocators used by Python: <ul class="simple"> <li><code class="docutils literal notranslate">default</code>: use the <a class="reference internal" href="../c-api/memory.html#default-memory-allocators">default memory allocators</a>.</li> <li><code class="docutils literal notranslate">malloc</code>: use the <code class="xref c c-func docutils literal notranslate">malloc()</code> function of the C library for all domains (<a class="reference internal" href="../c-api/memory.html#c.PYMEM_DOMAIN_RAW" title="PYMEM_DOMAIN_RAW"><code class="xref c c-macro docutils literal notranslate">PYMEM_DOMAIN_RAW</code></a>, <a class="reference internal" href="../c-api/memory.html#c.PYMEM_DOMAIN_MEM" title="PYMEM_DOMAIN_MEM"><code class="xref c c-macro docutils literal notranslate">PYMEM_DOMAIN_MEM</code></a>, <a class="reference internal" href="../c-api/memory.html#c.PYMEM_DOMAIN_OBJ" title="PYMEM_DOMAIN_OBJ"><code class="xref c c-macro docutils literal notranslate">PYMEM_DOMAIN_OBJ</code></a>).</li> <li><code class="docutils literal notranslate">pymalloc</code>: use the <a class="reference internal" href="../c-api/memory.html#pymalloc">pymalloc allocator</a> for <a class="reference internal" href="../c-api/memory.html#c.PYMEM_DOMAIN_MEM" title="PYMEM_DOMAIN_MEM"><code class="xref c c-macro docutils literal notranslate">PYMEM_DOMAIN_MEM</code></a> and <a class="reference internal" href="../c-api/memory.html#c.PYMEM_DOMAIN_OBJ" title="PYMEM_DOMAIN_OBJ"><code class="xref c c-macro docutils literal notranslate">PYMEM_DOMAIN_OBJ</code></a> domains and use the <code class="xref c c-func docutils literal notranslate">malloc()</code> function for the <a class="reference internal" href="../c-api/memory.html#c.PYMEM_DOMAIN_RAW" title="PYMEM_DOMAIN_RAW"><code class="xref c c-macro docutils literal notranslate">PYMEM_DOMAIN_RAW</code></a> domain.</li> <li><code class="docutils literal notranslate">mimalloc</code>: use the <a class="reference internal" href="../c-api/memory.html#mimalloc">mimalloc allocator</a> for <a class="reference internal" href="../c-api/memory.html#c.PYMEM_DOMAIN_MEM" title="PYMEM_DOMAIN_MEM"><code class="xref c c-macro docutils literal notranslate">PYMEM_DOMAIN_MEM</code></a> and <a class="reference internal" href="../c-api/memory.html#c.PYMEM_DOMAIN_OBJ" title="PYMEM_DOMAIN_OBJ"><code class="xref c c-macro docutils literal notranslate">PYMEM_DOMAIN_OBJ</code></a> domains and use the <code class="xref c c-func docutils literal notranslate">malloc()</code> function for the <a class="reference internal" href="../c-api/memory.html#c.PYMEM_DOMAIN_RAW" title="PYMEM_DOMAIN_RAW"><code class="xref c c-macro docutils literal notranslate">PYMEM_DOMAIN_RAW</code></a> domain.</li> </ul> Install <a class="reference internal" href="../c-api/memory.html#pymem-debug-hooks">debug hooks</a>: <ul class="simple"> <li><code class="docutils literal notranslate">debug</code>: install debug hooks on top of the <a class="reference internal" href="../c-api/memory.html#default-memory-allocators">default memory allocators</a>.</li> <li><code class="docutils literal notranslate">malloc_debug</code>: same as <code class="docutils literal notranslate">malloc</code> but also install debug hooks.</li> <li><code class="docutils literal notranslate">pymalloc_debug</code>: same as <code class="docutils literal notranslate">pymalloc</code> but also install debug hooks.</li> <li><code class="docutils literal notranslate">mimalloc_debug</code>: same as <code class="docutils literal notranslate">mimalloc</code> but also install debug hooks.</li> </ul> <div class="versionadded"> Added in version 3.6. </div> <div class="versionchanged"> Changed in version 3.7: Added the <code class="docutils literal notranslate">"default"</code> allocator. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONMALLOCSTATS"> PYTHONMALLOCSTATS<a class="headerlink" href="#envvar-PYTHONMALLOCSTATS" title="Link to this definition">¶</a></dt> <dd>If set to a non-empty string, Python will print statistics of the <a class="reference internal" href="../c-api/memory.html#pymalloc">pymalloc memory allocator</a> every time a new pymalloc object arena is created, and on shutdown. This variable is ignored if the <a class="reference internal" href="#envvar-PYTHONMALLOC"><code class="xref std std-envvar docutils literal notranslate">PYTHONMALLOC</code></a> environment variable is used to force the <code class="xref c c-func docutils literal notranslate">malloc()</code> allocator of the C library, or if Python is configured without <code class="docutils literal notranslate">pymalloc</code> support. <div class="versionchanged"> Changed in version 3.6: This variable can now also be used on Python compiled in release mode. It now has no effect if set to an empty string. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONLEGACYWINDOWSFSENCODING"> PYTHONLEGACYWINDOWSFSENCODING<a class="headerlink" href="#envvar-PYTHONLEGACYWINDOWSFSENCODING" title="Link to this definition">¶</a></dt> <dd>If set to a non-empty string, the default <a class="reference internal" href="../glossary.html#term-filesystem-encoding-and-error-handler">filesystem encoding and error handler</a> mode will revert to their pre-3.6 values of ‘mbcs’ and ‘replace’, respectively. Otherwise, the new defaults ‘utf-8’ and ‘surrogatepass’ are used. This may also be enabled at runtime with <a class="reference internal" href="../library/sys.html#sys._enablelegacywindowsfsencoding" title="sys._enablelegacywindowsfsencoding"><code class="xref py py-func docutils literal notranslate">sys._enablelegacywindowsfsencoding()</code></a>. <div class="availability docutils container"> <a class="reference internal" href="../library/intro.html#availability">Availability</a>: Windows. </div> <div class="versionadded"> Added in version 3.6: See <a class="pep reference external" href="https://peps.python.org/pep-0529/">PEP 529</a> for more details. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONLEGACYWINDOWSSTDIO"> PYTHONLEGACYWINDOWSSTDIO<a class="headerlink" href="#envvar-PYTHONLEGACYWINDOWSSTDIO" title="Link to this definition">¶</a></dt> <dd>If set to a non-empty string, does not use the new console reader and writer. This means that Unicode characters will be encoded according to the active console code page, rather than using utf-8. This variable is ignored if the standard streams are redirected (to files or pipes) rather than referring to console buffers. <div class="availability docutils container"> <a class="reference internal" href="../library/intro.html#availability">Availability</a>: Windows. </div> <div class="versionadded"> Added in version 3.6. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONCOERCECLOCALE"> PYTHONCOERCECLOCALE<a class="headerlink" href="#envvar-PYTHONCOERCECLOCALE" title="Link to this definition">¶</a></dt> <dd>If set to the value <code class="docutils literal notranslate">0</code>, causes the main Python command line application to skip coercing the legacy ASCII-based C and POSIX locales to a more capable UTF-8 based alternative. If this variable is not set (or is set to a value other than <code class="docutils literal notranslate">0</code>), the <code class="docutils literal notranslate">LC_ALL</code> locale override environment variable is also not set, and the current locale reported for the <code class="docutils literal notranslate">LC_CTYPE</code> category is either the default <code class="docutils literal notranslate">C</code> locale, or else the explicitly ASCII-based <code class="docutils literal notranslate">POSIX</code> locale, then the Python CLI will attempt to configure the following locales for the <code class="docutils literal notranslate">LC_CTYPE</code> category in the order listed before loading the interpreter runtime: <ul class="simple"> <li><code class="docutils literal notranslate">C.UTF-8</code></li> <li><code class="docutils literal notranslate">C.utf8</code></li> <li><code class="docutils literal notranslate">UTF-8</code></li> </ul> If setting one of these locale categories succeeds, then the <code class="docutils literal notranslate">LC_CTYPE</code> environment variable will also be set accordingly in the current process environment before the Python runtime is initialized. This ensures that in addition to being seen by both the interpreter itself and other locale-aware components running in the same process (such as the GNU <code class="docutils literal notranslate">readline</code> library), the updated setting is also seen in subprocesses (regardless of whether or not those processes are running a Python interpreter), as well as in operations that query the environment rather than the current C locale (such as Python’s own <a class="reference internal" href="../library/locale.html#locale.getdefaultlocale" title="locale.getdefaultlocale"><code class="xref py py-func docutils literal notranslate">locale.getdefaultlocale()</code></a>). Configuring one of these locales (either explicitly or via the above implicit locale coercion) automatically enables the <code class="docutils literal notranslate">surrogateescape</code> <a class="reference internal" href="../library/codecs.html#error-handlers">error handler</a> for <a class="reference internal" href="../library/sys.html#sys.stdin" title="sys.stdin"><code class="xref py py-data docutils literal notranslate">sys.stdin</code></a> and <a class="reference internal" href="../library/sys.html#sys.stdout" title="sys.stdout"><code class="xref py py-data docutils literal notranslate">sys.stdout</code></a> (<a class="reference internal" href="../library/sys.html#sys.stderr" title="sys.stderr"><code class="xref py py-data docutils literal notranslate">sys.stderr</code></a> continues to use <code class="docutils literal notranslate">backslashreplace</code> as it does in any other locale). This stream handling behavior can be overridden using <a class="reference internal" href="#envvar-PYTHONIOENCODING"><code class="xref std std-envvar docutils literal notranslate">PYTHONIOENCODING</code></a> as usual. For debugging purposes, setting <code class="docutils literal notranslate">PYTHONCOERCECLOCALE=warn</code> will cause Python to emit warning messages on <code class="docutils literal notranslate">stderr</code> if either the locale coercion activates, or else if a locale that would have triggered coercion is still active when the Python runtime is initialized. Also note that even when locale coercion is disabled, or when it fails to find a suitable target locale, <a class="reference internal" href="#envvar-PYTHONUTF8"><code class="xref std std-envvar docutils literal notranslate">PYTHONUTF8</code></a> will still activate by default in legacy ASCII-based locales. Both features must be disabled in order to force the interpreter to use <code class="docutils literal notranslate">ASCII</code> instead of <code class="docutils literal notranslate">UTF-8</code> for system interfaces. <div class="availability docutils container"> <a class="reference internal" href="../library/intro.html#availability">Availability</a>: Unix. </div> <div class="versionadded"> Added in version 3.7: See <a class="pep reference external" href="https://peps.python.org/pep-0538/">PEP 538</a> for more details. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONDEVMODE"> PYTHONDEVMODE<a class="headerlink" href="#envvar-PYTHONDEVMODE" title="Link to this definition">¶</a></dt> <dd>If this environment variable is set to a non-empty string, enable <a class="reference internal" href="../library/devmode.html#devmode">Python Development Mode</a>, introducing additional runtime checks that are too expensive to be enabled by default. This is equivalent to setting the <a class="reference internal" href="#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X</code></a> <code class="docutils literal notranslate">dev</code> option. <div class="versionadded"> Added in version 3.7. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONUTF8"> PYTHONUTF8<a class="headerlink" href="#envvar-PYTHONUTF8" title="Link to this definition">¶</a></dt> <dd>If set to <code class="docutils literal notranslate">1</code>, enable the <a class="reference internal" href="../library/os.html#utf8-mode">Python UTF-8 Mode</a>. If set to <code class="docutils literal notranslate">0</code>, disable the <a class="reference internal" href="../library/os.html#utf8-mode">Python UTF-8 Mode</a>. Setting any other non-empty string causes an error during interpreter initialisation. <div class="versionadded"> Added in version 3.7. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONWARNDEFAULTENCODING"> PYTHONWARNDEFAULTENCODING<a class="headerlink" href="#envvar-PYTHONWARNDEFAULTENCODING" title="Link to this definition">¶</a></dt> <dd>If this environment variable is set to a non-empty string, issue a <a class="reference internal" href="../library/exceptions.html#EncodingWarning" title="EncodingWarning"><code class="xref py py-class docutils literal notranslate">EncodingWarning</code></a> when the locale-specific default encoding is used. See <a class="reference internal" href="../library/io.html#io-encoding-warning">Opt-in EncodingWarning</a> for details. <div class="versionadded"> Added in version 3.10. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONNODEBUGRANGES"> PYTHONNODEBUGRANGES<a class="headerlink" href="#envvar-PYTHONNODEBUGRANGES" title="Link to this definition">¶</a></dt> <dd>If this variable is set, it disables the inclusion of the tables mapping extra location information (end line, start column offset and end column offset) to every instruction in code objects. This is useful when smaller code objects and pyc files are desired as well as suppressing the extra visual location indicators when the interpreter displays tracebacks. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONPERFSUPPORT"> PYTHONPERFSUPPORT<a class="headerlink" href="#envvar-PYTHONPERFSUPPORT" title="Link to this definition">¶</a></dt> <dd>If this variable is set to a nonzero value, it enables support for the Linux <code class="docutils literal notranslate">perf</code> profiler so Python calls can be detected by it. If set to <code class="docutils literal notranslate">0</code>, disable Linux <code class="docutils literal notranslate">perf</code> profiler support. See also the <a class="reference internal" href="#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X perf</code></a> command-line option and <a class="reference internal" href="../howto/perf_profiling.html#perf-profiling">Python support for the Linux perf profiler</a>. <div class="versionadded"> Added in version 3.12. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHON_PERF_JIT_SUPPORT"> PYTHON_PERF_JIT_SUPPORT<a class="headerlink" href="#envvar-PYTHON_PERF_JIT_SUPPORT" title="Link to this definition">¶</a></dt> <dd>If this variable is set to a nonzero value, it enables support for the Linux <code class="docutils literal notranslate">perf</code> profiler so Python calls can be detected by it using DWARF information. If set to <code class="docutils literal notranslate">0</code>, disable Linux <code class="docutils literal notranslate">perf</code> profiler support. See also the <a class="reference internal" href="#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X perf_jit</code></a> command-line option and <a class="reference internal" href="../howto/perf_profiling.html#perf-profiling">Python support for the Linux perf profiler</a>. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHON_CPU_COUNT"> PYTHON_CPU_COUNT<a class="headerlink" href="#envvar-PYTHON_CPU_COUNT" title="Link to this definition">¶</a></dt> <dd>If this variable is set to a positive integer, it overrides the return values of <a class="reference internal" href="../library/os.html#os.cpu_count" title="os.cpu_count"><code class="xref py py-func docutils literal notranslate">os.cpu_count()</code></a> and <a class="reference internal" href="../library/os.html#os.process_cpu_count" title="os.process_cpu_count"><code class="xref py py-func docutils literal notranslate">os.process_cpu_count()</code></a>. See also the <a class="reference internal" href="#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X cpu_count</code></a> command-line option. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHON_FROZEN_MODULES"> PYTHON_FROZEN_MODULES<a class="headerlink" href="#envvar-PYTHON_FROZEN_MODULES" title="Link to this definition">¶</a></dt> <dd>If this variable is set to <code class="docutils literal notranslate">on</code> or <code class="docutils literal notranslate">off</code>, it determines whether or not frozen modules are ignored by the import machinery. A value of <code class="docutils literal notranslate">on</code> means they get imported and <code class="docutils literal notranslate">off</code> means they are ignored. The default is <code class="docutils literal notranslate">on</code> for non-debug builds (the normal case) and <code class="docutils literal notranslate">off</code> for debug builds. Note that the <code class="xref py py-mod docutils literal notranslate">importlib_bootstrap</code> and <code class="xref py py-mod docutils literal notranslate">importlib_bootstrap_external</code> frozen modules are always used, even if this flag is set to <code class="docutils literal notranslate">off</code>. See also the <a class="reference internal" href="#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X frozen_modules</code></a> command-line option. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHON_COLORS"> PYTHON_COLORS<a class="headerlink" href="#envvar-PYTHON_COLORS" title="Link to this definition">¶</a></dt> <dd>If this variable is set to <code class="docutils literal notranslate">1</code>, the interpreter will colorize various kinds of output. Setting it to <code class="docutils literal notranslate">0</code> deactivates this behavior. See also <a class="reference internal" href="#using-on-controlling-color">Controlling color</a>. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHON_BASIC_REPL"> PYTHON_BASIC_REPL<a class="headerlink" href="#envvar-PYTHON_BASIC_REPL" title="Link to this definition">¶</a></dt> <dd>If this variable is set to <code class="docutils literal notranslate">1</code>, the interpreter will not attempt to load the Python-based <a class="reference internal" href="../glossary.html#term-REPL">REPL</a> that requires <a class="reference internal" href="../library/curses.html#module-curses" title="curses: An interface to the curses library, providing portable terminal handling. (Unix)"><code class="xref py py-mod docutils literal notranslate">curses</code></a> and <a class="reference internal" href="../library/readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><code class="xref py py-mod docutils literal notranslate">readline</code></a>, and will instead use the traditional parser-based <a class="reference internal" href="../glossary.html#term-REPL">REPL</a>. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHON_HISTORY"> PYTHON_HISTORY<a class="headerlink" href="#envvar-PYTHON_HISTORY" title="Link to this definition">¶</a></dt> <dd>This environment variable can be used to set the location of a <code class="docutils literal notranslate">.python_history</code> file (by default, it is <code class="docutils literal notranslate">.python_history</code> in the user’s home directory). <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHON_GIL"> PYTHON_GIL<a class="headerlink" href="#envvar-PYTHON_GIL" title="Link to this definition">¶</a></dt> <dd>If this variable is set to <code class="docutils literal notranslate">1</code>, the global interpreter lock (GIL) will be forced on. Setting it to <code class="docutils literal notranslate">0</code> forces the GIL off (needs Python configured with the <a class="reference internal" href="configure.html#cmdoption-disable-gil"><code class="xref std std-option docutils literal notranslate">--disable-gil</code></a> build option). See also the <a class="reference internal" href="#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X gil</code></a> command-line option, which takes precedence over this variable, and <a class="reference internal" href="../whatsnew/3.13.html#whatsnew313-free-threaded-cpython">Free-threaded CPython</a>. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <section id="debug-mode-variables"> <h3>1.2.1. Debug-mode variables<a class="headerlink" href="#debug-mode-variables" title="Link to this heading">¶</a></h3> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONDUMPREFS"> PYTHONDUMPREFS<a class="headerlink" href="#envvar-PYTHONDUMPREFS" title="Link to this definition">¶</a></dt> <dd>If set, Python will dump objects and reference counts still alive after shutting down the interpreter. Needs Python configured with the <a class="reference internal" href="configure.html#cmdoption-with-trace-refs"><code class="xref std std-option docutils literal notranslate">--with-trace-refs</code></a> build option. </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHONDUMPREFSFILE"> PYTHONDUMPREFSFILE<a class="headerlink" href="#envvar-PYTHONDUMPREFSFILE" title="Link to this definition">¶</a></dt> <dd>If set, Python will dump objects and reference counts still alive after shutting down the interpreter into a file under the path given as the value to this environment variable. Needs Python configured with the <a class="reference internal" href="configure.html#cmdoption-with-trace-refs"><code class="xref std std-option docutils literal notranslate">--with-trace-refs</code></a> build option. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="std envvar"> <dt class="sig sig-object std" id="envvar-PYTHON_PRESITE"> PYTHON_PRESITE<a class="headerlink" href="#envvar-PYTHON_PRESITE" title="Link to this definition">¶</a></dt> <dd>If this variable is set to a module, that module will be imported early in the interpreter lifecycle, before the <a class="reference internal" href="../library/site.html#module-site" title="site: Module responsible for site-specific configuration."><code class="xref py py-mod docutils literal notranslate">site</code></a> module is executed, and before the <a class="reference internal" href="../library/__main__.html#module-__main__" title="__main__: The environment where top-level code is run. Covers command-line interfaces, import-time behavior, and ``__name__ == '__main__'``."><code class="xref py py-mod docutils literal notranslate">__main__</code></a> module is created. Therefore, the imported module is not treated as <a class="reference internal" href="../library/__main__.html#module-__main__" title="__main__: The environment where top-level code is run. Covers command-line interfaces, import-time behavior, and ``__name__ == '__main__'``."><code class="xref py py-mod docutils literal notranslate">__main__</code></a>. This can be used to execute code early during Python initialization. To import a submodule, use <code class="docutils literal notranslate">package.module</code> as the value, like in an import statement. See also the <a class="reference internal" href="#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X presite</code></a> command-line option, which takes precedence over this variable. Needs Python configured with the <a class="reference internal" href="configure.html#cmdoption-with-pydebug"><code class="xref std std-option docutils literal notranslate">--with-pydebug</code></a> build option. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> </section> </section> </section> <div class="clearer"></div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="Main"> <div class="sphinxsidebarwrapper"> <div> <h3><a href="../contents.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#">1. Command line and environment</a><ul> <li><a class="reference internal" href="#command-line">1.1. Command line</a><ul> <li><a class="reference internal" href="#interface-options">1.1.1. Interface options</a></li> <li><a class="reference internal" href="#generic-options">1.1.2. Generic options</a></li> <li><a class="reference internal" href="#miscellaneous-options">1.1.3. Miscellaneous options</a></li> <li><a class="reference internal" href="#controlling-color">1.1.4. Controlling color</a></li> <li><a class="reference internal" href="#options-you-shouldn-t-use">1.1.5. Options you shouldn’t use</a></li> </ul> </li> <li><a class="reference internal" href="#environment-variables">1.2. Environment variables</a><ul> <li><a class="reference internal" href="#debug-mode-variables">1.2.1. Debug-mode variables</a></li> </ul> </li> </ul> </li> </ul> </div> <div> <h4>Previous topic</h4> <a href="index.html" title="previous chapter">Python Setup and Usage</a> </div> <div> <h4>Next topic</h4> <a href="unix.html" title="next chapter">2. 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