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3.9.20 Documentation
<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta charset="utf-8" /><title>3.9.20 Documentation</title><meta name="viewport" content="width=device-width, initial-scale=1.0"> <link rel="stylesheet" href="_static/pydoctheme.css" type="text/css" /> <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> <script id="documentation_options" data-url_root="./" src="_static/documentation_options.js"></script> <script src="_static/jquery.js"></script> <script src="_static/underscore.js"></script> <script src="_static/doctools.js"></script> <script src="_static/language_data.js"></script> <script src="_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.9.20 documentation" href="_static/opensearch.xml"/> <link rel="author" title="About these documents" href="about.html" /> <link rel="index" title="Index" href="genindex.html" /> <link rel="search" title="Search" href="search.html" /> <link rel="copyright" title="Copyright" href="copyright.html" /> <link rel="canonical" href="https://docs.python.org/3/index.html" /> <style> @media only screen { table.full-width-table { width: 100%; 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This is the official documentation for Python 3.9.20. </p> <p><strong>Parts of the documentation:</strong></p> <table class="contentstable" align="center"><tr> <td width="50%"> <p class="biglink"><a class="biglink" href="whatsnew/3.9.html">What's new in Python 3.9?</a><br/> <span class="linkdescr"> or <a href="whatsnew/index.html">all "What's new" documents</a> since 2.0</span></p> <p class="biglink"><a class="biglink" href="tutorial/index.html">Tutorial</a><br/> <span class="linkdescr">start here</span></p> <p class="biglink"><a class="biglink" href="library/index.html">Library Reference</a><br/> <span class="linkdescr">keep this under your pillow</span></p> <p class="biglink"><a class="biglink" href="reference/index.html">Language Reference</a><br/> <span class="linkdescr">describes syntax and language elements</span></p> <p class="biglink"><a class="biglink" href="using/index.html">Python Setup and Usage</a><br/> <span class="linkdescr">how to use Python on different platforms</span></p> <p class="biglink"><a class="biglink" href="howto/index.html">Python HOWTOs</a><br/> <span class="linkdescr">in-depth documents on specific topics</span></p> </td><td width="50%"> <p class="biglink"><a class="biglink" href="installing/index.html">Installing Python Modules</a><br/> <span class="linkdescr">installing from the Python Package Index & other sources</span></p> <p class="biglink"><a class="biglink" href="distributing/index.html">Distributing Python Modules</a><br/> <span class="linkdescr">publishing modules for installation by others</span></p> <p class="biglink"><a class="biglink" href="extending/index.html">Extending and Embedding</a><br/> <span class="linkdescr">tutorial for C/C++ programmers</span></p> <p class="biglink"><a class="biglink" href="c-api/index.html">Python/C API</a><br/> <span class="linkdescr">reference for C/C++ programmers</span></p> <p class="biglink"><a class="biglink" href="faq/index.html">FAQs</a><br/> <span class="linkdescr">frequently asked questions (with answers!)</span></p> </td></tr> </table> <p><strong>Indices and tables:</strong></p> <table class="contentstable" align="center"><tr> <td width="50%"> <p class="biglink"><a class="biglink" href="py-modindex.html">Global Module Index</a><br/> <span class="linkdescr">quick access to all modules</span></p> <p class="biglink"><a class="biglink" href="genindex.html">General Index</a><br/> <span class="linkdescr">all functions, classes, terms</span></p> <p class="biglink"><a class="biglink" href="glossary.html">Glossary</a><br/> <span class="linkdescr">the most important terms explained</span></p> </td><td width="50%"> <p class="biglink"><a class="biglink" href="search.html">Search page</a><br/> <span class="linkdescr">search this documentation</span></p> <p class="biglink"><a class="biglink" href="contents.html">Complete Table of Contents</a><br/> <span class="linkdescr">lists all sections and subsections</span></p> </td></tr> </table> <p><strong>Meta information:</strong></p> <table class="contentstable" align="center"><tr> <td width="50%"> <p class="biglink"><a class="biglink" href="bugs.html">Reporting bugs</a></p> <p class="biglink"><a class="biglink" href="https://devguide.python.org/docquality/#helping-with-documentation">Contributing to Docs</a></p> <p class="biglink"><a class="biglink" href="about.html">About the documentation</a></p> </td><td width="50%"> <p class="biglink"><a class="biglink" href="license.html">History and License of Python</a></p> <p class="biglink"><a class="biglink" href="copyright.html">Copyright</a></p> </td></tr> </table> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3>Download</h3> <p><a href="download.html">Download these documents</a></p> <h3>Docs by version</h3> <ul> <li><a href="https://docs.python.org/3.14/">Python 3.14 (in development)</a></li> <li><a href="https://docs.python.org/3.13/">Python 3.13 (pre-release)</a></li> <li><a href="https://docs.python.org/3.12/">Python 3.12 (stable)</a></li> <li><a href="https://docs.python.org/3.11/">Python 3.11 (security-fixes)</a></li> <li><a href="https://docs.python.org/3.10/">Python 3.10 (security-fixes)</a></li> <li><a href="https://docs.python.org/3.9/">Python 3.9 (security-fixes)</a></li> <li><a href="https://docs.python.org/3.8/">Python 3.8 (security-fixes)</a></li> <li><a href="https://docs.python.org/3.7/">Python 3.7 (EOL)</a></li> <li><a href="https://docs.python.org/3.6/">Python 3.6 (EOL)</a></li> <li><a href="https://docs.python.org/3.5/">Python 3.5 (EOL)</a></li> <li><a href="https://docs.python.org/3.4/">Python 3.4 (EOL)</a></li> <li><a href="https://docs.python.org/3.3/">Python 3.3 (EOL)</a></li> <li><a href="https://docs.python.org/3.2/">Python 3.2 (EOL)</a></li> <li><a href="https://docs.python.org/3.1/">Python 3.1 (EOL)</a></li> <li><a href="https://docs.python.org/3.0/">Python 3.0 (EOL)</a></li> <li><a href="https://docs.python.org/2.7/">Python 2.7 (EOL)</a></li> <li><a href="https://docs.python.org/2.6/">Python 2.6 (EOL)</a></li> <li><a href="https://www.python.org/doc/versions/">All versions</a></li> </ul> <h3>Other resources</h3> <ul> <li><a href="https://peps.python.org">PEP Index</a></li> <li><a href="https://wiki.python.org/moin/BeginnersGuide">Beginner's Guide</a></li> <li><a href="https://wiki.python.org/moin/PythonBooks">Book List</a></li> <li><a href="https://www.python.org/doc/av/">Audio/Visual Talks</a></li> <li><a href="https://devguide.python.org/">Python Developer鈥檚 Guide</a></li> </ul> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="py-modindex.html" title="Python 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