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<div class="section" id="command-line-and-environment">
<span id="using-on-general"></span><h1>1. Command line and environment<a class="headerlink" href="#command-line-and-environment" title="Permalink to this headline">¶</a></h1>
<p>The CPython interpreter scans the command line and the environment for various
settings.</p>
<div class="impl-detail compound">
<p><strong>CPython implementation detail:</strong> Other implementations’ command line schemes may differ. See
<a class="reference internal" href="../reference/introduction.html#implementations"><em>Alternate Implementations</em></a> for further resources.</p>
</div>
<div class="section" id="command-line">
<span id="using-on-cmdline"></span><h2>1.1. Command line<a class="headerlink" href="#command-line" title="Permalink to this headline">¶</a></h2>
<p>When invoking Python, you may specify any of these options:</p>
<div class="highlight-none"><div class="highlight"><pre>python [-BdEiOQsRStuUvVWxX3?] [-c command | -m module-name | script | - ] [args]
</pre></div>
</div>
<p>The most common use case is, of course, a simple invocation of a script:</p>
<div class="highlight-none"><div class="highlight"><pre>python myscript.py
</pre></div>
</div>
<div class="section" id="interface-options">
<span id="using-on-interface-options"></span><h3>1.1.1. Interface options<a class="headerlink" href="#interface-options" title="Permalink to this headline">¶</a></h3>
<p>The interpreter interface resembles that of the UNIX shell, but provides some
additional methods of invocation:</p>
<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 <em>Ctrl-D</em> on UNIX or <em>Ctrl-Z, Enter</em> on Windows) is read.</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 <tt class="docutils literal"><span class="pre">-c</span> <span class="pre">command</span></tt>, it executes the Python statement(s) given as
<em>command</em>. Here <em>command</em> may contain multiple statements separated by
newlines. Leading whitespace is significant in Python statements!</li>
<li>When called with <tt class="docutils literal"><span class="pre">-m</span> <span class="pre">module-name</span></tt>, the given module is located on the
Python module path and executed as a script.</li>
</ul>
<p>In non-interactive mode, the entire input is parsed before it is executed.</p>
<p>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"><tt class="xref py py-data docutils literal"><span class="pre">sys.argv</span></tt></a> – note that the first
element, subscript zero (<tt class="docutils literal"><span class="pre">sys.argv[0]</span></tt>), is a string reflecting the program’s
source.</p>
<dl class="cmdoption">
<dt id="cmdoption-c">
<tt class="descname">-c</tt><tt class="descclassname"> <command></tt><a class="headerlink" href="#cmdoption-c" title="Permalink to this definition">¶</a></dt>
<dd><p>Execute the Python code in <em>command</em>. <em>command</em> can be one or more
statements separated by newlines, with significant leading whitespace as in
normal module code.</p>
<p>If this option is given, the first element of <a class="reference internal" href="../library/sys.html#sys.argv" title="sys.argv"><tt class="xref py py-data docutils literal"><span class="pre">sys.argv</span></tt></a> will be
<tt class="docutils literal"><span class="pre">"-c"</span></tt> and the current directory will be added to the start of
<a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a> (allowing modules in that directory to be imported as top
level modules).</p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-m">
<tt class="descname">-m</tt><tt class="descclassname"> <module-name></tt><a class="headerlink" href="#cmdoption-m" title="Permalink to this definition">¶</a></dt>
<dd><p>Search <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></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 the top-level script is run."><tt class="xref py py-mod docutils literal"><span class="pre">__main__</span></tt></a> module.</p>
<p>Since the argument is a <em>module</em> name, you must not give a file extension
(<tt class="docutils literal"><span class="pre">.py</span></tt>). The <tt class="docutils literal"><span class="pre">module-name</span></tt> should be a valid 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).</p>
<p>Package names are also permitted. When a package name is supplied instead
of a normal module, the interpreter will execute <tt class="docutils literal"><span class="pre"><pkg>.__main__</span></tt> 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.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">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.</p>
</div>
<p>If this option is given, the first element of <a class="reference internal" href="../library/sys.html#sys.argv" title="sys.argv"><tt class="xref py py-data docutils literal"><span class="pre">sys.argv</span></tt></a> will be the
full path to the module file. As with the <a class="reference internal" href="#cmdoption-c"><em class="xref std std-option">-c</em></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"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>.</p>
<p>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."><tt class="xref py py-mod docutils literal"><span class="pre">timeit</span></tt></a> module:</p>
<div class="highlight-none"><div class="highlight"><pre>python -mtimeit -s 'setup here' 'benchmarked code here'
python -mtimeit -h # for details
</pre></div>
</div>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<p><a class="reference internal" href="../library/runpy.html#runpy.run_module" title="runpy.run_module"><tt class="xref py py-func docutils literal"><span class="pre">runpy.run_module()</span></tt></a>
Equivalent functionality directly available to Python code</p>
<p class="last"><span class="target" id="index-0"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0338"><strong>PEP 338</strong></a> – Executing modules as scripts</p>
</div>
<p class="versionadded">
<span class="versionmodified">New in version 2.4.</span></p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.5: </span>The named module can now be located inside a package.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.7: </span>Supply the package name to run a <tt class="docutils literal"><span class="pre">__main__</span></tt> submodule.
sys.argv[0] is now set to <tt class="docutils literal"><span class="pre">"-m"</span></tt> while searching for the module
(it was previously incorrectly set to <tt class="docutils literal"><span class="pre">"-c"</span></tt>)</p>
</dd></dl>
<dl class="describe">
<dt>
<tt class="descname">-</tt></dt>
<dd><p>Read commands from standard input (<a class="reference internal" href="../library/sys.html#sys.stdin" title="sys.stdin"><tt class="xref py py-data docutils literal"><span class="pre">sys.stdin</span></tt></a>). If standard input is
a terminal, <a class="reference internal" href="#cmdoption-i"><em class="xref std std-option">-i</em></a> is implied.</p>
<p>If this option is given, the first element of <a class="reference internal" href="../library/sys.html#sys.argv" title="sys.argv"><tt class="xref py py-data docutils literal"><span class="pre">sys.argv</span></tt></a> will be
<tt class="docutils literal"><span class="pre">"-"</span></tt> and the current directory will be added to the start of
<a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>.</p>
</dd></dl>
<dl class="describe">
<dt>
<tt class="descname"><script></tt></dt>
<dd><p>Execute the Python code contained in <em>script</em>, which must be a filesystem
path (absolute or relative) referring to either a Python file, a directory
containing a <tt class="docutils literal"><span class="pre">__main__.py</span></tt> file, or a zipfile containing a
<tt class="docutils literal"><span class="pre">__main__.py</span></tt> file.</p>
<p>If this option is given, the first element of <a class="reference internal" href="../library/sys.html#sys.argv" title="sys.argv"><tt class="xref py py-data docutils literal"><span class="pre">sys.argv</span></tt></a> will be the
script name as given on the command line.</p>
<p>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"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>, and the
file is executed as the <a class="reference internal" href="../library/__main__.html#module-__main__" title="__main__: The environment where the top-level script is run."><tt class="xref py py-mod docutils literal"><span class="pre">__main__</span></tt></a> module.</p>
<p>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"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a> and the <tt class="docutils literal"><span class="pre">__main__.py</span></tt> file in
that location is executed as the <a class="reference internal" href="../library/__main__.html#module-__main__" title="__main__: The environment where the top-level script is run."><tt class="xref py py-mod docutils literal"><span class="pre">__main__</span></tt></a> module.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.5: </span>Directories and zipfiles containing a <tt class="docutils literal"><span class="pre">__main__.py</span></tt> file at the top
level are now considered valid Python scripts.</p>
</dd></dl>
<p>If no interface option is given, <a class="reference internal" href="#cmdoption-i"><em class="xref std std-option">-i</em></a> is implied, <tt class="docutils literal"><span class="pre">sys.argv[0]</span></tt> is
an empty string (<tt class="docutils literal"><span class="pre">""</span></tt>) and the current directory will be added to the
start of <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>.</p>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last"><a class="reference internal" href="../tutorial/interpreter.html#tut-invoking"><em>Invoking the Interpreter</em></a></p>
</div>
</div>
<div class="section" id="generic-options">
<h3>1.1.2. Generic options<a class="headerlink" href="#generic-options" title="Permalink to this headline">¶</a></h3>
<dl class="cmdoption">
<dt>
<tt class="descname">-?</tt></dt>
<dt id="cmdoption-h">
<tt class="descname">-h</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-h" title="Permalink to this definition">¶</a></dt>
<dt id="cmdoption--help">
<tt class="descname">--help</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption--help" title="Permalink to this definition">¶</a></dt>
<dd><p>Print a short description of all command line options.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.5: </span>The <tt class="docutils literal"><span class="pre">--help</span></tt> variant.</p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-V">
<tt class="descname">-V</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-V" title="Permalink to this definition">¶</a></dt>
<dt id="cmdoption--version">
<tt class="descname">--version</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption--version" title="Permalink to this definition">¶</a></dt>
<dd><p>Print the Python version number and exit. Example output could be:</p>
<div class="highlight-none"><div class="highlight"><pre>Python 2.5.1
</pre></div>
</div>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.5: </span>The <tt class="docutils literal"><span class="pre">--version</span></tt> variant.</p>
</dd></dl>
</div>
<div class="section" id="miscellaneous-options">
<h3>1.1.3. Miscellaneous options<a class="headerlink" href="#miscellaneous-options" title="Permalink to this headline">¶</a></h3>
<dl class="cmdoption">
<dt id="cmdoption-B">
<tt class="descname">-B</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-B" title="Permalink to this definition">¶</a></dt>
<dd><p>If given, Python won’t try to write <tt class="docutils literal"><span class="pre">.pyc</span></tt> or <tt class="docutils literal"><span class="pre">.pyo</span></tt> files on the
import of source modules. See also <span class="target" id="index-1"></span><a class="reference internal" href="#envvar-PYTHONDONTWRITEBYTECODE"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONDONTWRITEBYTECODE</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-d">
<tt class="descname">-d</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-d" title="Permalink to this definition">¶</a></dt>
<dd><p>Turn on parser debugging output (for wizards only, depending on compilation
options). See also <span class="target" id="index-2"></span><a class="reference internal" href="#envvar-PYTHONDEBUG"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONDEBUG</span></tt></a>.</p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-E">
<tt class="descname">-E</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-E" title="Permalink to this definition">¶</a></dt>
<dd><p>Ignore all <span class="target" id="index-3"></span><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHON*</span></tt> environment variables, e.g.
<span class="target" id="index-4"></span><a class="reference internal" href="#envvar-PYTHONPATH"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONPATH</span></tt></a> and <span class="target" id="index-5"></span><a class="reference internal" href="#envvar-PYTHONHOME"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONHOME</span></tt></a>, that might be set.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.2.</span></p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-i">
<tt class="descname">-i</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-i" title="Permalink to this definition">¶</a></dt>
<dd><p>When a script is passed as first argument or the <a class="reference internal" href="#cmdoption-c"><em class="xref std std-option">-c</em></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"><tt class="xref py py-data docutils literal"><span class="pre">sys.stdin</span></tt></a> does not appear to be a terminal. The
<span class="target" id="index-6"></span><a class="reference internal" href="#envvar-PYTHONSTARTUP"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONSTARTUP</span></tt></a> file is not read.</p>
<p>This can be useful to inspect global variables or a stack trace when a script
raises an exception. See also <span class="target" id="index-7"></span><a class="reference internal" href="#envvar-PYTHONINSPECT"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONINSPECT</span></tt></a>.</p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-O">
<tt class="descname">-O</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-O" title="Permalink to this definition">¶</a></dt>
<dd><p>Turn on basic optimizations. This changes the filename extension for
compiled (<a class="reference internal" href="../glossary.html#term-bytecode"><em class="xref std std-term">bytecode</em></a>) files from <tt class="docutils literal"><span class="pre">.pyc</span></tt> to <tt class="docutils literal"><span class="pre">.pyo</span></tt>. See also
<span class="target" id="index-8"></span><a class="reference internal" href="#envvar-PYTHONOPTIMIZE"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONOPTIMIZE</span></tt></a>.</p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-OO">
<tt class="descname">-OO</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-OO" title="Permalink to this definition">¶</a></dt>
<dd><p>Discard docstrings in addition to the <a class="reference internal" href="#cmdoption-O"><em class="xref std std-option">-O</em></a> optimizations.</p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-Q">
<tt class="descname">-Q</tt><tt class="descclassname"> <arg></tt><a class="headerlink" href="#cmdoption-Q" title="Permalink to this definition">¶</a></dt>
<dd><p>Division control. The argument must be one of the following:</p>
<dl class="docutils">
<dt><tt class="docutils literal"><span class="pre">old</span></tt></dt>
<dd>division of int/int and long/long return an int or long (<em>default</em>)</dd>
<dt><tt class="docutils literal"><span class="pre">new</span></tt></dt>
<dd>new division semantics, i.e. division of int/int and long/long returns a
float</dd>
<dt><tt class="docutils literal"><span class="pre">warn</span></tt></dt>
<dd>old division semantics with a warning for int/int and long/long</dd>
<dt><tt class="docutils literal"><span class="pre">warnall</span></tt></dt>
<dd>old division semantics with a warning for all uses of the division operator</dd>
</dl>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<p><tt class="file docutils literal"><span class="pre">Tools/scripts/fixdiv.py</span></tt>
for a use of <tt class="docutils literal"><span class="pre">warnall</span></tt></p>
<p class="last"><span class="target" id="index-9"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0238"><strong>PEP 238</strong></a> – Changing the division operator</p>
</div>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-R">
<tt class="descname">-R</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-R" title="Permalink to this definition">¶</a></dt>
<dd><p>Turn on hash randomization, so that the <a class="reference internal" href="../reference/datamodel.html#object.__hash__" title="object.__hash__"><tt class="xref py py-meth docutils literal"><span class="pre">__hash__()</span></tt></a> values of str,
bytes and datetime 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.</p>
<p>This 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(n^2) complexity. See
<a class="reference external" href="http://www.ocert.org/advisories/ocert-2011-003.html">http://www.ocert.org/advisories/ocert-2011-003.html</a> for details.</p>
<p>Changing hash values affects the order in which keys are retrieved from a
dict. Although Python has never made guarantees about this ordering (and it
typically varies between 32-bit and 64-bit builds), enough real-world code
implicitly relies on this non-guaranteed behavior that the randomization is
disabled by default.</p>
<p>See also <span class="target" id="index-10"></span><a class="reference internal" href="#envvar-PYTHONHASHSEED"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONHASHSEED</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.8.</span></p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-s">
<tt class="descname">-s</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-s" title="Permalink to this definition">¶</a></dt>
<dd><p>Don’t add the <a class="reference internal" href="../library/site.html#site.USER_SITE" title="site.USER_SITE"><tt class="xref py py-data docutils literal"><span class="pre">user</span> <span class="pre">site-packages</span> <span class="pre">directory</span></tt></a> to
<a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last"><span class="target" id="index-11"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0370"><strong>PEP 370</strong></a> – Per user site-packages directory</p>
</div>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-S">
<tt class="descname">-S</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-S" title="Permalink to this definition">¶</a></dt>
<dd><p>Disable the import of the module <a class="reference internal" href="../library/site.html#module-site" title="site: Module responsible for site-specific configuration."><tt class="xref py py-mod docutils literal"><span class="pre">site</span></tt></a> and the site-dependent
manipulations of <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a> that it entails.</p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-t">
<tt class="descname">-t</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-t" title="Permalink to this definition">¶</a></dt>
<dd><p>Issue a warning when a source file mixes tabs and spaces for indentation in a
way that makes it depend on the worth of a tab expressed in spaces. Issue an
error when the option is given twice (<em class="xref std std-option">-tt</em>).</p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-u">
<tt class="descname">-u</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-u" title="Permalink to this definition">¶</a></dt>
<dd><p>Force stdin, stdout and stderr to be totally unbuffered. On systems where it
matters, also put stdin, stdout and stderr in binary mode.</p>
<p>Note that there is internal buffering in <a class="reference internal" href="../library/stdtypes.html#file.readlines" title="file.readlines"><tt class="xref py py-meth docutils literal"><span class="pre">file.readlines()</span></tt></a> and
<a class="reference internal" href="../library/stdtypes.html#bltin-file-objects"><em>File Objects</em></a> (<tt class="docutils literal"><span class="pre">for</span> <span class="pre">line</span> <span class="pre">in</span> <span class="pre">sys.stdin</span></tt>) which is not influenced
by this option. To work around this, you will want to use
<a class="reference internal" href="../library/stdtypes.html#file.readline" title="file.readline"><tt class="xref py py-meth docutils literal"><span class="pre">file.readline()</span></tt></a> inside a <tt class="docutils literal"><span class="pre">while</span> <span class="pre">1:</span></tt> loop.</p>
<p>See also <span class="target" id="index-12"></span><a class="reference internal" href="#envvar-PYTHONUNBUFFERED"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONUNBUFFERED</span></tt></a>.</p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-v">
<tt class="descname">-v</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-v" title="Permalink to this definition">¶</a></dt>
<dd><p>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
(<em class="xref std std-option">-vv</em>), print a message for each file that is checked for when
searching for a module. Also provides information on module cleanup at exit.
See also <span class="target" id="index-13"></span><a class="reference internal" href="#envvar-PYTHONVERBOSE"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONVERBOSE</span></tt></a>.</p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-W">
<tt class="descname">-W</tt><tt class="descclassname"> arg</tt><a class="headerlink" href="#cmdoption-W" title="Permalink to this definition">¶</a></dt>
<dd><p>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"><tt class="xref py py-data docutils literal"><span class="pre">sys.stderr</span></tt></a>. A typical warning message has the following
form:</p>
<div class="highlight-none"><div class="highlight"><pre>file:line: category: message
</pre></div>
</div>
<p>By default, each warning is printed once for each source line where it
occurs. This option controls how often warnings are printed.</p>
<p>Multiple <a class="reference internal" href="#cmdoption-W"><em class="xref std std-option">-W</em></a> options may 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"><em class="xref std std-option">-W</em></a> options are ignored (though, a warning message is printed about
invalid options when the first warning is issued).</p>
<p>Starting from Python 2.7, <a class="reference internal" href="../library/exceptions.html#exceptions.DeprecationWarning" title="exceptions.DeprecationWarning"><tt class="xref py py-exc docutils literal"><span class="pre">DeprecationWarning</span></tt></a> and its descendants
are ignored by default. The <em class="xref std std-option">-Wd</em> option can be used to re-enable
them.</p>
<p>Warnings can also be controlled 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."><tt class="xref py py-mod docutils literal"><span class="pre">warnings</span></tt></a> module.</p>
<p>The simplest form of argument is one of the following action strings (or a
unique abbreviation) by themselves:</p>
<dl class="docutils">
<dt><tt class="docutils literal"><span class="pre">ignore</span></tt></dt>
<dd>Ignore all warnings.</dd>
<dt><tt class="docutils literal"><span class="pre">default</span></tt></dt>
<dd>Explicitly request the default behavior (printing each warning once per
source line).</dd>
<dt><tt class="docutils literal"><span class="pre">all</span></tt></dt>
<dd>Print a warning each time it occurs (this may generate many messages if a
warning is triggered repeatedly for the same source line, such as inside a
loop).</dd>
<dt><tt class="docutils literal"><span class="pre">module</span></tt></dt>
<dd>Print each warning only the first time it occurs in each module.</dd>
<dt><tt class="docutils literal"><span class="pre">once</span></tt></dt>
<dd>Print each warning only the first time it occurs in the program.</dd>
<dt><tt class="docutils literal"><span class="pre">error</span></tt></dt>
<dd>Raise an exception instead of printing a warning message.</dd>
</dl>
<p>The full form of argument is:</p>
<div class="highlight-none"><div class="highlight"><pre>action:message:category:module:line
</pre></div>
</div>
<p>Here, <em>action</em> is as explained above but only applies to messages that match
the remaining fields. Empty fields match all values; trailing empty fields
may be omitted. The <em>message</em> field matches the start of the warning message
printed; this match is case-insensitive. The <em>category</em> field matches the
warning category. This must be a class name; the match tests whether the
actual warning category of the message is a subclass of the specified warning
category. The full class name must be given. The <em>module</em> field matches the
(fully-qualified) module name; this match is case-sensitive. The <em>line</em>
field matches the line number, where zero matches all line numbers and is
thus equivalent to an omitted line number.</p>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<p><a class="reference internal" href="../library/warnings.html#module-warnings" title="warnings: Issue warning messages and control their disposition."><tt class="xref py py-mod docutils literal"><span class="pre">warnings</span></tt></a> – the warnings module</p>
<p><span class="target" id="index-14"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0230"><strong>PEP 230</strong></a> – Warning framework</p>
<p class="last"><span class="target" id="index-15"></span><a class="reference internal" href="#envvar-PYTHONWARNINGS"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONWARNINGS</span></tt></a></p>
</div>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-x">
<tt class="descname">-x</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-x" title="Permalink to this definition">¶</a></dt>
<dd><p>Skip the first line of the source, allowing use of non-Unix forms of
<tt class="docutils literal"><span class="pre">#!cmd</span></tt>. This is intended for a DOS specific hack only.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The line numbers in error messages will be off by one.</p>
</div>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-3">
<tt class="descname">-3</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-3" title="Permalink to this definition">¶</a></dt>
<dd><p>Warn about Python 3.x incompatibilities which cannot be fixed trivially by
<a class="reference internal" href="../library/2to3.html#to3-reference"><em>2to3</em></a>. Among these are:</p>
<ul class="simple">
<li><a class="reference internal" href="../library/stdtypes.html#dict.has_key" title="dict.has_key"><tt class="xref py py-meth docutils literal"><span class="pre">dict.has_key()</span></tt></a></li>
<li><a class="reference internal" href="../library/functions.html#apply" title="apply"><tt class="xref py py-func docutils literal"><span class="pre">apply()</span></tt></a></li>
<li><a class="reference internal" href="../library/functions.html#callable" title="callable"><tt class="xref py py-func docutils literal"><span class="pre">callable()</span></tt></a></li>
<li><a class="reference internal" href="../library/functions.html#coerce" title="coerce"><tt class="xref py py-func docutils literal"><span class="pre">coerce()</span></tt></a></li>
<li><a class="reference internal" href="../library/functions.html#execfile" title="execfile"><tt class="xref py py-func docutils literal"><span class="pre">execfile()</span></tt></a></li>
<li><a class="reference internal" href="../library/functions.html#reduce" title="reduce"><tt class="xref py py-func docutils literal"><span class="pre">reduce()</span></tt></a></li>
<li><a class="reference internal" href="../library/functions.html#reload" title="reload"><tt class="xref py py-func docutils literal"><span class="pre">reload()</span></tt></a></li>
</ul>
<p>Using these will emit a <a class="reference internal" href="../library/exceptions.html#exceptions.DeprecationWarning" title="exceptions.DeprecationWarning"><tt class="xref py py-exc docutils literal"><span class="pre">DeprecationWarning</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
</dd></dl>
</div>
<div class="section" id="options-you-shouldn-t-use">
<h3>1.1.4. Options you shouldn’t use<a class="headerlink" href="#options-you-shouldn-t-use" title="Permalink to this headline">¶</a></h3>
<dl class="cmdoption">
<dt id="cmdoption-J">
<tt class="descname">-J</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-J" title="Permalink to this definition">¶</a></dt>
<dd><p>Reserved for use by <a class="reference external" href="http://jython.org">Jython</a>.</p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-U">
<tt class="descname">-U</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-U" title="Permalink to this definition">¶</a></dt>
<dd><p>Turns all string literals into unicodes globally. Do not be tempted to use
this option as it will probably break your world. It also produces
<tt class="docutils literal"><span class="pre">.pyc</span></tt> files with a different magic number than normal. Instead, you can
enable unicode literals on a per-module basis by using:</p>
<div class="highlight-none"><div class="highlight"><pre>from __future__ import unicode_literals
</pre></div>
</div>
<p>at the top of the file. See <a class="reference internal" href="../library/__future__.html#module-__future__" title="__future__: Future statement definitions"><tt class="xref py py-mod docutils literal"><span class="pre">__future__</span></tt></a> for details.</p>
</dd></dl>
<dl class="cmdoption">
<dt id="cmdoption-X">
<tt class="descname">-X</tt><tt class="descclassname"></tt><a class="headerlink" href="#cmdoption-X" title="Permalink to this definition">¶</a></dt>
<dd><p>Reserved for alternative implementations of Python to use for their own
purposes.</p>
</dd></dl>
</div>
</div>
<div class="section" id="environment-variables">
<span id="using-on-envvars"></span><h2>1.2. Environment variables<a class="headerlink" href="#environment-variables" title="Permalink to this headline">¶</a></h2>
<p>These environment variables influence Python’s behavior, they are processed
before the command-line switches other than -E. It is customary that
command-line switches override environmental variables where there is a
conflict.</p>
<dl class="envvar">
<dt id="envvar-PYTHONHOME">
<tt class="descname">PYTHONHOME</tt><a class="headerlink" href="#envvar-PYTHONHOME" title="Permalink to this definition">¶</a></dt>
<dd><p>Change the location of the standard Python libraries. By default, the
libraries are searched in <tt class="file docutils literal"><em><span class="pre">prefix</span></em><span class="pre">/lib/python</span><em><span class="pre">version</span></em></tt> and
<tt class="file docutils literal"><em><span class="pre">exec_prefix</span></em><span class="pre">/lib/python</span><em><span class="pre">version</span></em></tt>, where <tt class="file docutils literal"><em><span class="pre">prefix</span></em></tt> and
<tt class="file docutils literal"><em><span class="pre">exec_prefix</span></em></tt> are installation-dependent directories, both defaulting
to <tt class="file docutils literal"><span class="pre">/usr/local</span></tt>.</p>
<p>When <span class="target" id="index-16"></span><a class="reference internal" href="#envvar-PYTHONHOME"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONHOME</span></tt></a> is set to a single directory, its value replaces
both <tt class="file docutils literal"><em><span class="pre">prefix</span></em></tt> and <tt class="file docutils literal"><em><span class="pre">exec_prefix</span></em></tt>. To specify different values
for these, set <span class="target" id="index-17"></span><a class="reference internal" href="#envvar-PYTHONHOME"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONHOME</span></tt></a> to <tt class="file docutils literal"><em><span class="pre">prefix</span></em><span class="pre">:</span><em><span class="pre">exec_prefix</span></em></tt>.</p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONPATH">
<tt class="descname">PYTHONPATH</tt><a class="headerlink" href="#envvar-PYTHONPATH" title="Permalink to this definition">¶</a></dt>
<dd><p>Augment the default search path for module files. The format is the same as
the shell’s <span class="target" id="index-18"></span><tt class="xref std std-envvar docutils literal"><span class="pre">PATH</span></tt>: one or more directory pathnames separated by
<a class="reference internal" href="../library/os.html#os.pathsep" title="os.pathsep"><tt class="xref py py-data docutils literal"><span class="pre">os.pathsep</span></tt></a> (e.g. colons on Unix or semicolons on Windows).
Non-existent directories are silently ignored.</p>
<p>In addition to normal directories, individual <span class="target" id="index-19"></span><a class="reference internal" href="#envvar-PYTHONPATH"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONPATH</span></tt></a> entries
may refer to zipfiles containing pure Python modules (in either source or
compiled form). Extension modules cannot be imported from zipfiles.</p>
<p>The default search path is installation dependent, but generally begins with
<tt class="file docutils literal"><em><span class="pre">prefix</span></em><span class="pre">/lib/python</span><em><span class="pre">version</span></em></tt> (see <span class="target" id="index-20"></span><a class="reference internal" href="#envvar-PYTHONHOME"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONHOME</span></tt></a> above). It
is <em>always</em> appended to <span class="target" id="index-21"></span><a class="reference internal" href="#envvar-PYTHONPATH"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONPATH</span></tt></a>.</p>
<p>An additional directory will be inserted in the search path in front of
<span class="target" id="index-22"></span><a class="reference internal" href="#envvar-PYTHONPATH"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONPATH</span></tt></a> as described above under
<a class="reference internal" href="#using-on-interface-options"><em>Interface options</em></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"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>.</p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONSTARTUP">
<tt class="descname">PYTHONSTARTUP</tt><a class="headerlink" href="#envvar-PYTHONSTARTUP" title="Permalink to this definition">¶</a></dt>
<dd><p>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"><tt class="xref py py-data docutils literal"><span class="pre">sys.ps1</span></tt></a> and
<a class="reference internal" href="../library/sys.html#sys.ps2" title="sys.ps2"><tt class="xref py py-data docutils literal"><span class="pre">sys.ps2</span></tt></a> in this file.</p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONY2K">
<tt class="descname">PYTHONY2K</tt><a class="headerlink" href="#envvar-PYTHONY2K" title="Permalink to this definition">¶</a></dt>
<dd><p>Set this to a non-empty string to cause the <a class="reference internal" href="../library/time.html#module-time" title="time: Time access and conversions."><tt class="xref py py-mod docutils literal"><span class="pre">time</span></tt></a> module to require
dates specified as strings to include 4-digit years, otherwise 2-digit years
are converted based on rules described in the <a class="reference internal" href="../library/time.html#module-time" title="time: Time access and conversions."><tt class="xref py py-mod docutils literal"><span class="pre">time</span></tt></a> module
documentation.</p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONOPTIMIZE">
<tt class="descname">PYTHONOPTIMIZE</tt><a class="headerlink" href="#envvar-PYTHONOPTIMIZE" title="Permalink to this definition">¶</a></dt>
<dd><p>If this is set to a non-empty string it is equivalent to specifying the
<a class="reference internal" href="#cmdoption-O"><em class="xref std std-option">-O</em></a> option. If set to an integer, it is equivalent to specifying
<a class="reference internal" href="#cmdoption-O"><em class="xref std std-option">-O</em></a> multiple times.</p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONDEBUG">
<tt class="descname">PYTHONDEBUG</tt><a class="headerlink" href="#envvar-PYTHONDEBUG" title="Permalink to this definition">¶</a></dt>
<dd><p>If this is set to a non-empty string it is equivalent to specifying the
<a class="reference internal" href="#cmdoption-d"><em class="xref std std-option">-d</em></a> option. If set to an integer, it is equivalent to specifying
<a class="reference internal" href="#cmdoption-d"><em class="xref std std-option">-d</em></a> multiple times.</p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONINSPECT">
<tt class="descname">PYTHONINSPECT</tt><a class="headerlink" href="#envvar-PYTHONINSPECT" title="Permalink to this definition">¶</a></dt>
<dd><p>If this is set to a non-empty string it is equivalent to specifying the
<a class="reference internal" href="#cmdoption-i"><em class="xref std std-option">-i</em></a> option.</p>
<p>This variable can also be modified by Python code using <a class="reference internal" href="../library/os.html#os.environ" title="os.environ"><tt class="xref py py-data docutils literal"><span class="pre">os.environ</span></tt></a>
to force inspect mode on program termination.</p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONUNBUFFERED">
<tt class="descname">PYTHONUNBUFFERED</tt><a class="headerlink" href="#envvar-PYTHONUNBUFFERED" title="Permalink to this definition">¶</a></dt>
<dd><p>If this is set to a non-empty string it is equivalent to specifying the
<a class="reference internal" href="#cmdoption-u"><em class="xref std std-option">-u</em></a> option.</p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONVERBOSE">
<tt class="descname">PYTHONVERBOSE</tt><a class="headerlink" href="#envvar-PYTHONVERBOSE" title="Permalink to this definition">¶</a></dt>
<dd><p>If this is set to a non-empty string it is equivalent to specifying the
<a class="reference internal" href="#cmdoption-v"><em class="xref std std-option">-v</em></a> option. If set to an integer, it is equivalent to specifying
<a class="reference internal" href="#cmdoption-v"><em class="xref std std-option">-v</em></a> multiple times.</p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONCASEOK">
<tt class="descname">PYTHONCASEOK</tt><a class="headerlink" href="#envvar-PYTHONCASEOK" title="Permalink to this definition">¶</a></dt>
<dd><p>If this is set, Python ignores case in <a class="reference internal" href="../reference/simple_stmts.html#import"><tt class="xref std std-keyword docutils literal"><span class="pre">import</span></tt></a> statements. This
only works on Windows, OS X, OS/2, and RiscOS.</p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONDONTWRITEBYTECODE">
<tt class="descname">PYTHONDONTWRITEBYTECODE</tt><a class="headerlink" href="#envvar-PYTHONDONTWRITEBYTECODE" title="Permalink to this definition">¶</a></dt>
<dd><p>If this is set, Python won’t try to write <tt class="docutils literal"><span class="pre">.pyc</span></tt> or <tt class="docutils literal"><span class="pre">.pyo</span></tt> files on the
import of source modules. This is equivalent to specifying the <a class="reference internal" href="#cmdoption-B"><em class="xref std std-option">-B</em></a>
option.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONHASHSEED">
<tt class="descname">PYTHONHASHSEED</tt><a class="headerlink" href="#envvar-PYTHONHASHSEED" title="Permalink to this definition">¶</a></dt>
<dd><p>If this variable is set to <tt class="docutils literal"><span class="pre">random</span></tt>, the effect is the same as specifying
the <a class="reference internal" href="#cmdoption-R"><em class="xref std std-option">-R</em></a> option: a random value is used to seed the hashes of str,
bytes and datetime objects.</p>
<p>If <span class="target" id="index-23"></span><a class="reference internal" href="#envvar-PYTHONHASHSEED"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONHASHSEED</span></tt></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.</p>
<p>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.</p>
<p>The integer must be a decimal number in the range [0,4294967295].
Specifying the value 0 will lead to the same hash values as when hash
randomization is disabled.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.8.</span></p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONIOENCODING">
<tt class="descname">PYTHONIOENCODING</tt><a class="headerlink" href="#envvar-PYTHONIOENCODING" title="Permalink to this definition">¶</a></dt>
<dd><p>Overrides the encoding used for stdin/stdout/stderr, in the syntax
<tt class="docutils literal"><span class="pre">encodingname:errorhandler</span></tt>. The <tt class="docutils literal"><span class="pre">:errorhandler</span></tt> part is optional and
has the same meaning as in <a class="reference internal" href="../library/stdtypes.html#str.encode" title="str.encode"><tt class="xref py py-func docutils literal"><span class="pre">str.encode()</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONNOUSERSITE">
<tt class="descname">PYTHONNOUSERSITE</tt><a class="headerlink" href="#envvar-PYTHONNOUSERSITE" title="Permalink to this definition">¶</a></dt>
<dd><p>If this is set, Python won’t add the <a class="reference internal" href="../library/site.html#site.USER_SITE" title="site.USER_SITE"><tt class="xref py py-data docutils literal"><span class="pre">user</span> <span class="pre">site-packages</span> <span class="pre">directory</span></tt></a> to <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last"><span class="target" id="index-24"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0370"><strong>PEP 370</strong></a> – Per user site-packages directory</p>
</div>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONUSERBASE">
<tt class="descname">PYTHONUSERBASE</tt><a class="headerlink" href="#envvar-PYTHONUSERBASE" title="Permalink to this definition">¶</a></dt>
<dd><p>Defines the <a class="reference internal" href="../library/site.html#site.USER_BASE" title="site.USER_BASE"><tt class="xref py py-data docutils literal"><span class="pre">user</span> <span class="pre">base</span> <span class="pre">directory</span></tt></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"><tt class="xref py py-data docutils literal"><span class="pre">user</span> <span class="pre">site-packages</span> <span class="pre">directory</span></tt></a>
and <a class="reference internal" href="../install/index.html#inst-alt-install-user"><em>Distutils installation paths</em></a> for <tt class="docutils literal"><span class="pre">python</span>
<span class="pre">setup.py</span> <span class="pre">install</span> <span class="pre">--user</span></tt>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last"><span class="target" id="index-25"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0370"><strong>PEP 370</strong></a> – Per user site-packages directory</p>
</div>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONEXECUTABLE">
<tt class="descname">PYTHONEXECUTABLE</tt><a class="headerlink" href="#envvar-PYTHONEXECUTABLE" title="Permalink to this definition">¶</a></dt>
<dd><p>If this environment variable is set, <tt class="docutils literal"><span class="pre">sys.argv[0]</span></tt> will be set to its
value instead of the value got through the C runtime. Only works on
Mac OS X.</p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONWARNINGS">
<tt class="descname">PYTHONWARNINGS</tt><a class="headerlink" href="#envvar-PYTHONWARNINGS" title="Permalink to this definition">¶</a></dt>
<dd><p>This is equivalent to the <a class="reference internal" href="#cmdoption-W"><em class="xref std std-option">-W</em></a> option. If set to a comma
separated string, it is equivalent to specifying <a class="reference internal" href="#cmdoption-W"><em class="xref std std-option">-W</em></a> multiple
times.</p>
</dd></dl>
<div class="section" id="debug-mode-variables">
<h3>1.2.1. Debug-mode variables<a class="headerlink" href="#debug-mode-variables" title="Permalink to this headline">¶</a></h3>
<p>Setting these variables only has an effect in a debug build of Python, that is,
if Python was configured with the <tt class="docutils literal"><span class="pre">--with-pydebug</span></tt> build option.</p>
<dl class="envvar">
<dt id="envvar-PYTHONTHREADDEBUG">
<tt class="descname">PYTHONTHREADDEBUG</tt><a class="headerlink" href="#envvar-PYTHONTHREADDEBUG" title="Permalink to this definition">¶</a></dt>
<dd><p>If set, Python will print threading debug info.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.6: </span>Previously, this variable was called <tt class="docutils literal"><span class="pre">THREADDEBUG</span></tt>.</p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONDUMPREFS">
<tt class="descname">PYTHONDUMPREFS</tt><a class="headerlink" href="#envvar-PYTHONDUMPREFS" title="Permalink to this definition">¶</a></dt>
<dd><p>If set, Python will dump objects and reference counts still alive after
shutting down the interpreter.</p>
</dd></dl>
<dl class="envvar">
<dt id="envvar-PYTHONMALLOCSTATS">
<tt class="descname">PYTHONMALLOCSTATS</tt><a class="headerlink" href="#envvar-PYTHONMALLOCSTATS" title="Permalink to this definition">¶</a></dt>
<dd><p>If set, Python will print memory allocation statistics every time a new
object arena is created, and on shutdown.</p>
</dd></dl>
</div>
</div>
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<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="#options-you-shouldn-t-use">1.1.4. 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>
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