mirror of
https://github.com/bunny-lab-io/Borealis.git
synced 2025-11-03 19:41:57 -07:00
433 lines
22 KiB
HTML
433 lines
22 KiB
HTML
<!DOCTYPE html>
|
||
|
||
<html lang="en" data-content_root="../">
|
||
<head>
|
||
<meta charset="utf-8" />
|
||
<meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="viewport" content="width=device-width, initial-scale=1" />
|
||
<meta property="og:title" content="1. Introduction" />
|
||
<meta property="og:type" content="website" />
|
||
<meta property="og:url" content="https://docs.python.org/3/reference/introduction.html" />
|
||
<meta property="og:site_name" content="Python documentation" />
|
||
<meta property="og:description" content="This reference manual describes the Python programming language. It is not intended as a tutorial. While I am trying to be as precise as possible, I chose to use English rather than formal specific..." />
|
||
<meta property="og:image" content="https://docs.python.org/3/_static/og-image.png" />
|
||
<meta property="og:image:alt" content="Python documentation" />
|
||
<meta name="description" content="This reference manual describes the Python programming language. It is not intended as a tutorial. While I am trying to be as precise as possible, I chose to use English rather than formal specific..." />
|
||
<meta property="og:image:width" content="200">
|
||
<meta property="og:image:height" content="200">
|
||
<meta name="theme-color" content="#3776ab">
|
||
|
||
<title>1. Introduction — Python 3.13.3 documentation</title><meta name="viewport" content="width=device-width, initial-scale=1.0">
|
||
|
||
<link rel="stylesheet" type="text/css" href="../_static/pygments.css?v=b86133f3" />
|
||
<link rel="stylesheet" type="text/css" href="../_static/pydoctheme.css?v=23252803" />
|
||
<link id="pygments_dark_css" media="(prefers-color-scheme: dark)" rel="stylesheet" type="text/css" href="../_static/pygments_dark.css?v=5349f25f" />
|
||
|
||
<script src="../_static/documentation_options.js?v=5d57ca2d"></script>
|
||
<script src="../_static/doctools.js?v=9bcbadda"></script>
|
||
<script src="../_static/sphinx_highlight.js?v=dc90522c"></script>
|
||
|
||
<script src="../_static/sidebar.js"></script>
|
||
|
||
<link rel="search" type="application/opensearchdescription+xml"
|
||
title="Search within Python 3.13.3 documentation"
|
||
href="../_static/opensearch.xml"/>
|
||
<link rel="author" title="About these documents" href="../about.html" />
|
||
<link rel="index" title="Index" href="../genindex.html" />
|
||
<link rel="search" title="Search" href="../search.html" />
|
||
<link rel="copyright" title="Copyright" href="../copyright.html" />
|
||
<link rel="next" title="2. Lexical analysis" href="lexical_analysis.html" />
|
||
<link rel="prev" title="The Python Language Reference" href="index.html" />
|
||
|
||
<link rel="canonical" href="https://docs.python.org/3/reference/introduction.html">
|
||
|
||
|
||
|
||
|
||
|
||
<style>
|
||
@media only screen {
|
||
table.full-width-table {
|
||
width: 100%;
|
||
}
|
||
}
|
||
</style>
|
||
<link rel="stylesheet" href="../_static/pydoctheme_dark.css" media="(prefers-color-scheme: dark)" id="pydoctheme_dark_css">
|
||
<link rel="shortcut icon" type="image/png" href="../_static/py.svg" />
|
||
<script type="text/javascript" src="../_static/copybutton.js"></script>
|
||
<script type="text/javascript" src="../_static/menu.js"></script>
|
||
<script type="text/javascript" src="../_static/search-focus.js"></script>
|
||
<script type="text/javascript" src="../_static/themetoggle.js"></script>
|
||
<script type="text/javascript" src="../_static/rtd_switcher.js"></script>
|
||
<meta name="readthedocs-addons-api-version" content="1">
|
||
|
||
</head>
|
||
<body>
|
||
<div class="mobile-nav">
|
||
<input type="checkbox" id="menuToggler" class="toggler__input" aria-controls="navigation"
|
||
aria-pressed="false" aria-expanded="false" role="button" aria-label="Menu" />
|
||
<nav class="nav-content" role="navigation">
|
||
<label for="menuToggler" class="toggler__label">
|
||
<span></span>
|
||
</label>
|
||
<span class="nav-items-wrapper">
|
||
<a href="https://www.python.org/" class="nav-logo">
|
||
<img src="../_static/py.svg" alt="Python logo"/>
|
||
</a>
|
||
<span class="version_switcher_placeholder"></span>
|
||
<form role="search" class="search" action="../search.html" method="get">
|
||
<svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" class="search-icon">
|
||
<path fill-rule="nonzero" fill="currentColor" d="M15.5 14h-.79l-.28-.27a6.5 6.5 0 001.48-5.34c-.47-2.78-2.79-5-5.59-5.34a6.505 6.505 0 00-7.27 7.27c.34 2.8 2.56 5.12 5.34 5.59a6.5 6.5 0 005.34-1.48l.27.28v.79l4.25 4.25c.41.41 1.08.41 1.49 0 .41-.41.41-1.08 0-1.49L15.5 14zm-6 0C7.01 14 5 11.99 5 9.5S7.01 5 9.5 5 14 7.01 14 9.5 11.99 14 9.5 14z"></path>
|
||
</svg>
|
||
<input placeholder="Quick search" aria-label="Quick search" type="search" name="q" />
|
||
<input type="submit" value="Go"/>
|
||
</form>
|
||
</span>
|
||
</nav>
|
||
<div class="menu-wrapper">
|
||
<nav class="menu" role="navigation" aria-label="main navigation">
|
||
<div class="language_switcher_placeholder"></div>
|
||
|
||
<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>
|
||
<div>
|
||
<h3><a href="../contents.html">Table of Contents</a></h3>
|
||
<ul>
|
||
<li><a class="reference internal" href="#">1. Introduction</a><ul>
|
||
<li><a class="reference internal" href="#alternate-implementations">1.1. Alternate Implementations</a></li>
|
||
<li><a class="reference internal" href="#notation">1.2. Notation</a></li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
|
||
</div>
|
||
<div>
|
||
<h4>Previous topic</h4>
|
||
<p class="topless"><a href="index.html"
|
||
title="previous chapter">The Python Language Reference</a></p>
|
||
</div>
|
||
<div>
|
||
<h4>Next topic</h4>
|
||
<p class="topless"><a href="lexical_analysis.html"
|
||
title="next chapter"><span class="section-number">2. </span>Lexical analysis</a></p>
|
||
</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/reference/introduction.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="lexical_analysis.html" title="2. Lexical analysis"
|
||
accesskey="N">next</a> |</li>
|
||
<li class="right" >
|
||
<a href="index.html" title="The Python Language Reference"
|
||
accesskey="P">previous</a> |</li>
|
||
|
||
<li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"/></li>
|
||
<li><a href="https://www.python.org/">Python</a> »</li>
|
||
<li class="switchers">
|
||
<div class="language_switcher_placeholder"></div>
|
||
<div class="version_switcher_placeholder"></div>
|
||
</li>
|
||
<li>
|
||
|
||
</li>
|
||
<li id="cpython-language-and-version">
|
||
<a href="../index.html">3.13.3 Documentation</a> »
|
||
</li>
|
||
|
||
<li class="nav-item nav-item-1"><a href="index.html" accesskey="U">The Python Language Reference</a> »</li>
|
||
<li class="nav-item nav-item-this"><a href=""><span class="section-number">1. </span>Introduction</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="introduction">
|
||
<span id="id1"></span><h1><span class="section-number">1. </span>Introduction<a class="headerlink" href="#introduction" title="Link to this heading">¶</a></h1>
|
||
<p>This reference manual describes the Python programming language. It is not
|
||
intended as a tutorial.</p>
|
||
<p>While I am trying to be as precise as possible, I chose to use English rather
|
||
than formal specifications for everything except syntax and lexical analysis.
|
||
This should make the document more understandable to the average reader, but
|
||
will leave room for ambiguities. Consequently, if you were coming from Mars and
|
||
tried to re-implement Python from this document alone, you might have to guess
|
||
things and in fact you would probably end up implementing quite a different
|
||
language. On the other hand, if you are using Python and wonder what the precise
|
||
rules about a particular area of the language are, you should definitely be able
|
||
to find them here. If you would like to see a more formal definition of the
|
||
language, maybe you could volunteer your time — or invent a cloning machine
|
||
:-).</p>
|
||
<p>It is dangerous to add too many implementation details to a language reference
|
||
document — the implementation may change, and other implementations of the
|
||
same language may work differently. On the other hand, CPython is the one
|
||
Python implementation in widespread use (although alternate implementations
|
||
continue to gain support), and its particular quirks are sometimes worth being
|
||
mentioned, especially where the implementation imposes additional limitations.
|
||
Therefore, you’ll find short “implementation notes” sprinkled throughout the
|
||
text.</p>
|
||
<p>Every Python implementation comes with a number of built-in and standard
|
||
modules. These are documented in <a class="reference internal" href="../library/index.html#library-index"><span class="std std-ref">The Python Standard Library</span></a>. A few built-in modules
|
||
are mentioned when they interact in a significant way with the language
|
||
definition.</p>
|
||
<section id="alternate-implementations">
|
||
<span id="implementations"></span><h2><span class="section-number">1.1. </span>Alternate Implementations<a class="headerlink" href="#alternate-implementations" title="Link to this heading">¶</a></h2>
|
||
<p>Though there is one Python implementation which is by far the most popular,
|
||
there are some alternate implementations which are of particular interest to
|
||
different audiences.</p>
|
||
<p>Known implementations include:</p>
|
||
<dl class="simple">
|
||
<dt>CPython</dt><dd><p>This is the original and most-maintained implementation of Python, written in C.
|
||
New language features generally appear here first.</p>
|
||
</dd>
|
||
<dt>Jython</dt><dd><p>Python implemented in Java. This implementation can be used as a scripting
|
||
language for Java applications, or can be used to create applications using the
|
||
Java class libraries. It is also often used to create tests for Java libraries.
|
||
More information can be found at <a class="reference external" href="https://www.jython.org/">the Jython website</a>.</p>
|
||
</dd>
|
||
<dt>Python for .NET</dt><dd><p>This implementation actually uses the CPython implementation, but is a managed
|
||
.NET application and makes .NET libraries available. It was created by Brian
|
||
Lloyd. For more information, see the <a class="reference external" href="https://pythonnet.github.io/">Python for .NET home page</a>.</p>
|
||
</dd>
|
||
<dt>IronPython</dt><dd><p>An alternate Python for .NET. Unlike Python.NET, this is a complete Python
|
||
implementation that generates IL, and compiles Python code directly to .NET
|
||
assemblies. It was created by Jim Hugunin, the original creator of Jython. For
|
||
more information, see <a class="reference external" href="https://ironpython.net/">the IronPython website</a>.</p>
|
||
</dd>
|
||
<dt>PyPy</dt><dd><p>An implementation of Python written completely in Python. It supports several
|
||
advanced features not found in other implementations like stackless support
|
||
and a Just in Time compiler. One of the goals of the project is to encourage
|
||
experimentation with the language itself by making it easier to modify the
|
||
interpreter (since it is written in Python). Additional information is
|
||
available on <a class="reference external" href="https://pypy.org/">the PyPy project’s home page</a>.</p>
|
||
</dd>
|
||
</dl>
|
||
<p>Each of these implementations varies in some way from the language as documented
|
||
in this manual, or introduces specific information beyond what’s covered in the
|
||
standard Python documentation. Please refer to the implementation-specific
|
||
documentation to determine what else you need to know about the specific
|
||
implementation you’re using.</p>
|
||
</section>
|
||
<section id="notation">
|
||
<span id="id2"></span><h2><span class="section-number">1.2. </span>Notation<a class="headerlink" href="#notation" title="Link to this heading">¶</a></h2>
|
||
<p id="index-0">The descriptions of lexical analysis and syntax use a modified
|
||
<a class="reference external" href="https://en.wikipedia.org/wiki/Backus%E2%80%93Naur_form">Backus–Naur form (BNF)</a> grammar
|
||
notation. This uses the following style of definition:</p>
|
||
<pre>
|
||
<strong id="grammar-token-notation-name">name</strong> ::= <a class="reference internal" href="#grammar-token-notation-lc_letter"><code class="xref docutils literal notranslate"><span class="pre">lc_letter</span></code></a> (<a class="reference internal" href="#grammar-token-notation-lc_letter"><code class="xref docutils literal notranslate"><span class="pre">lc_letter</span></code></a> | "_")*
|
||
<strong id="grammar-token-notation-lc_letter">lc_letter</strong> ::= "a"..."z"
|
||
</pre>
|
||
<p>The first line says that a <code class="docutils literal notranslate"><span class="pre">name</span></code> is an <code class="docutils literal notranslate"><span class="pre">lc_letter</span></code> followed by a sequence
|
||
of zero or more <code class="docutils literal notranslate"><span class="pre">lc_letter</span></code>s and underscores. An <code class="docutils literal notranslate"><span class="pre">lc_letter</span></code> in turn is
|
||
any of the single characters <code class="docutils literal notranslate"><span class="pre">'a'</span></code> through <code class="docutils literal notranslate"><span class="pre">'z'</span></code>. (This rule is actually
|
||
adhered to for the names defined in lexical and grammar rules in this document.)</p>
|
||
<p>Each rule begins with a name (which is the name defined by the rule) and
|
||
<code class="docutils literal notranslate"><span class="pre">::=</span></code>. A vertical bar (<code class="docutils literal notranslate"><span class="pre">|</span></code>) is used to separate alternatives; it is the
|
||
least binding operator in this notation. A star (<code class="docutils literal notranslate"><span class="pre">*</span></code>) means zero or more
|
||
repetitions of the preceding item; likewise, a plus (<code class="docutils literal notranslate"><span class="pre">+</span></code>) means one or more
|
||
repetitions, and a phrase enclosed in square brackets (<code class="docutils literal notranslate"><span class="pre">[</span> <span class="pre">]</span></code>) means zero or
|
||
one occurrences (in other words, the enclosed phrase is optional). The <code class="docutils literal notranslate"><span class="pre">*</span></code>
|
||
and <code class="docutils literal notranslate"><span class="pre">+</span></code> operators bind as tightly as possible; parentheses are used for
|
||
grouping. Literal strings are enclosed in quotes. White space is only
|
||
meaningful to separate tokens. Rules are normally contained on a single line;
|
||
rules with many alternatives may be formatted alternatively with each line after
|
||
the first beginning with a vertical bar.</p>
|
||
<p id="index-1">In lexical definitions (as the example above), two more conventions are used:
|
||
Two literal characters separated by three dots mean a choice of any single
|
||
character in the given (inclusive) range of ASCII characters. A phrase between
|
||
angular brackets (<code class="docutils literal notranslate"><span class="pre"><...></span></code>) gives an informal description of the symbol
|
||
defined; e.g., this could be used to describe the notion of ‘control character’
|
||
if needed.</p>
|
||
<p>Even though the notation used is almost the same, there is a big difference
|
||
between the meaning of lexical and syntactic definitions: a lexical definition
|
||
operates on the individual characters of the input source, while a syntax
|
||
definition operates on the stream of tokens generated by the lexical analysis.
|
||
All uses of BNF in the next chapter (“Lexical Analysis”) are lexical
|
||
definitions; uses in subsequent chapters are syntactic definitions.</p>
|
||
</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. Introduction</a><ul>
|
||
<li><a class="reference internal" href="#alternate-implementations">1.1. Alternate Implementations</a></li>
|
||
<li><a class="reference internal" href="#notation">1.2. Notation</a></li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
|
||
</div>
|
||
<div>
|
||
<h4>Previous topic</h4>
|
||
<p class="topless"><a href="index.html"
|
||
title="previous chapter">The Python Language Reference</a></p>
|
||
</div>
|
||
<div>
|
||
<h4>Next topic</h4>
|
||
<p class="topless"><a href="lexical_analysis.html"
|
||
title="next chapter"><span class="section-number">2. </span>Lexical analysis</a></p>
|
||
</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/reference/introduction.rst"
|
||
rel="nofollow">Show Source
|
||
</a>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
</div>
|
||
<div id="sidebarbutton" title="Collapse sidebar">
|
||
<span>«</span>
|
||
</div>
|
||
|
||
</div>
|
||
<div class="clearer"></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"
|
||
>index</a></li>
|
||
<li class="right" >
|
||
<a href="../py-modindex.html" title="Python Module Index"
|
||
>modules</a> |</li>
|
||
<li class="right" >
|
||
<a href="lexical_analysis.html" title="2. Lexical analysis"
|
||
>next</a> |</li>
|
||
<li class="right" >
|
||
<a href="index.html" title="The Python Language Reference"
|
||
>previous</a> |</li>
|
||
|
||
<li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"/></li>
|
||
<li><a href="https://www.python.org/">Python</a> »</li>
|
||
<li class="switchers">
|
||
<div class="language_switcher_placeholder"></div>
|
||
<div class="version_switcher_placeholder"></div>
|
||
</li>
|
||
<li>
|
||
|
||
</li>
|
||
<li id="cpython-language-and-version">
|
||
<a href="../index.html">3.13.3 Documentation</a> »
|
||
</li>
|
||
|
||
<li class="nav-item nav-item-1"><a href="index.html" >The Python Language Reference</a> »</li>
|
||
<li class="nav-item nav-item-this"><a href=""><span class="section-number">1. </span>Introduction</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="footer">
|
||
©
|
||
<a href="../copyright.html">
|
||
|
||
Copyright
|
||
|
||
</a>
|
||
2001-2025, Python Software Foundation.
|
||
<br />
|
||
This page is licensed under the Python Software Foundation License Version 2.
|
||
<br />
|
||
Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License.
|
||
<br />
|
||
|
||
See <a href="/license.html">History and License</a> for more information.<br />
|
||
|
||
|
||
<br />
|
||
|
||
The Python Software Foundation is a non-profit corporation.
|
||
<a href="https://www.python.org/psf/donations/">Please donate.</a>
|
||
<br />
|
||
<br />
|
||
Last updated on Apr 08, 2025 (14:33 UTC).
|
||
|
||
<a href="/bugs.html">Found a bug</a>?
|
||
|
||
<br />
|
||
|
||
Created using <a href="https://www.sphinx-doc.org/">Sphinx</a> 8.2.3.
|
||
</div>
|
||
|
||
</body>
|
||
</html> |