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<H1><A NAME="SECTION0010100000000000000000"></A><A NAME="programs"></A>
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<BR>
8.1 Complete Python programs
</H1>

<P>
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 <tt class="module">sys</tt>
(various system services), <tt class="module">__builtin__</tt> (built-in functions,
exceptions and <code>None</code>) and <tt class="module">__main__</tt>.  The latter is used
to provide the local and global namespace for execution of the
complete program.
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<P>
The syntax for a complete Python program is that for file input,
described in the next section.

<P>
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 <tt class="module">__main__</tt>.
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<P>
Under <span class="Unix">Unix</span>, a complete program can be passed to the interpreter in
three forms: with the <b class="programopt">-c</b> <var>string</var> 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.
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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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