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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="X-UA-Compatible" content="IE=Edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>9. Top-level components — Python 3.6.7 documentation</title> <link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.6.7 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="10. Full Grammar specification" href="grammar.html" /> <link rel="prev" title="8. Compound statements" href="compound_stmts.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/reference/toplevel_components.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <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" 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="grammar.html" title="10. Full Grammar specification" accesskey="N">next</a> |</li> <li class="right" > <a href="compound_stmts.html" title="8. Compound statements" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">3.6.7 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" accesskey="U">The Python Language Reference</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="top-level-components"> <span id="top-level"></span><h1>9. Top-level components<a class="headerlink" href="#top-level-components" title="Permalink to this headline">¶</a></h1> <p id="index-0">The Python interpreter can get its input from a number of sources: from a script passed to it as standard input or as program argument, typed in interactively, from a module source file, etc. This chapter gives the syntax used in these cases.</p> <div class="section" id="complete-python-programs"> <span id="programs"></span><h2>9.1. Complete Python programs<a class="headerlink" href="#complete-python-programs" title="Permalink to this headline">¶</a></h2> <span class="target" id="index-1"></span><p id="index-2">While a language specification need not prescribe how the language interpreter is invoked, it is useful to have a notion of a complete Python program. A complete Python program is executed in a minimally initialized environment: all built-in and standard modules are available, but none have been initialized, except for <a class="reference internal" href="../library/sys.html#module-sys" title="sys: Access system-specific parameters and functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">sys</span></code></a> (various system services), <a class="reference internal" href="../library/builtins.html#module-builtins" title="builtins: The module that provides the built-in namespace."><code class="xref py py-mod docutils literal notranslate"><span class="pre">builtins</span></code></a> (built-in functions, exceptions and <code class="docutils literal notranslate"><span class="pre">None</span></code>) and <a class="reference internal" href="../library/__main__.html#module-__main__" title="__main__: The environment where the top-level script is run."><code class="xref py py-mod docutils literal notranslate"><span class="pre">__main__</span></code></a>. The latter is used to provide the local and global namespace for execution of the complete program.</p> <p>The syntax for a complete Python program is that for file input, described in the next section.</p> <p id="index-3">The interpreter may also be invoked in interactive mode; in this case, it does not read and execute a complete program but reads and executes one statement (possibly compound) at a time. The initial environment is identical to that of a complete program; each statement is executed in the namespace of <a class="reference internal" href="../library/__main__.html#module-__main__" title="__main__: The environment where the top-level script is run."><code class="xref py py-mod docutils literal notranslate"><span class="pre">__main__</span></code></a>.</p> <p id="index-4">A complete program can be passed to the interpreter in three forms: with the <a class="reference internal" href="../using/cmdline.html#cmdoption-c"><code class="xref std std-option docutils literal notranslate"><span class="pre">-c</span></code></a> <em>string</em> command line option, as a file passed as the first command line argument, or as standard input. If the file or standard input is a tty device, the interpreter enters interactive mode; otherwise, it executes the file as a complete program.</p> </div> <div class="section" id="file-input"> <span id="id1"></span><h2>9.2. File input<a class="headerlink" href="#file-input" title="Permalink to this headline">¶</a></h2> <p>All input read from non-interactive files has the same form:</p> <pre> <strong id="grammar-token-file_input">file_input</strong> ::= (NEWLINE | <a class="reference internal" href="compound_stmts.html#grammar-token-statement"><code class="xref docutils literal notranslate"><span class="pre">statement</span></code></a>)* </pre> <p>This syntax is used in the following situations:</p> <ul class="simple"> <li>when parsing a complete Python program (from a file or from a string);</li> <li>when parsing a module;</li> <li>when parsing a string passed to the <a class="reference internal" href="../library/functions.html#exec" title="exec"><code class="xref py py-func docutils literal notranslate"><span class="pre">exec()</span></code></a> function;</li> </ul> </div> <div class="section" id="interactive-input"> <span id="interactive"></span><h2>9.3. Interactive input<a class="headerlink" href="#interactive-input" title="Permalink to this headline">¶</a></h2> <p>Input in interactive mode is parsed using the following grammar:</p> <pre> <strong id="grammar-token-interactive_input">interactive_input</strong> ::= [<a class="reference internal" href="compound_stmts.html#grammar-token-stmt_list"><code class="xref docutils literal notranslate"><span class="pre">stmt_list</span></code></a>] NEWLINE | <a class="reference internal" href="compound_stmts.html#grammar-token-compound_stmt"><code class="xref docutils literal notranslate"><span class="pre">compound_stmt</span></code></a> NEWLINE </pre> <p>Note that a (top-level) compound statement must be followed by a blank line in interactive mode; this is needed to help the parser detect the end of the input.</p> </div> <div class="section" id="expression-input"> <span id="id2"></span><h2>9.4. Expression input<a class="headerlink" href="#expression-input" title="Permalink to this headline">¶</a></h2> <span class="target" id="index-5"></span><p id="index-6"><a class="reference internal" href="../library/functions.html#eval" title="eval"><code class="xref py py-func docutils literal notranslate"><span class="pre">eval()</span></code></a> is used for expression input. It ignores leading whitespace. The string argument to <a class="reference internal" href="../library/functions.html#eval" title="eval"><code class="xref py py-func docutils literal notranslate"><span class="pre">eval()</span></code></a> must have the following form:</p> <pre> <strong id="grammar-token-eval_input">eval_input</strong> ::= <a class="reference internal" href="expressions.html#grammar-token-expression_list"><code class="xref docutils literal notranslate"><span class="pre">expression_list</span></code></a> NEWLINE* </pre> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">9. Top-level components</a><ul> <li><a class="reference internal" href="#complete-python-programs">9.1. Complete Python programs</a></li> <li><a class="reference internal" href="#file-input">9.2. File input</a></li> <li><a class="reference internal" href="#interactive-input">9.3. Interactive input</a></li> <li><a class="reference internal" href="#expression-input">9.4. Expression input</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="compound_stmts.html" title="previous chapter">8. Compound statements</a></p> <h4>Next topic</h4> <p class="topless"><a href="grammar.html" title="next chapter">10. 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