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| 55 | <H1><A NAME="SECTION0010100000000000000000"></A><A NAME="programs"></A> |
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| 58 | 8.1 Complete Python programs |
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| 60 | |
| 61 | <P> |
| 62 | While a language specification need not prescribe how the language |
| 63 | interpreter is invoked, it is useful to have a notion of a complete |
| 64 | Python program. A complete Python program is executed in a minimally |
| 65 | initialized environment: all built-in and standard modules are |
| 66 | available, but none have been initialized, except for <tt class="module">sys</tt> |
| 67 | (various system services), <tt class="module">__builtin__</tt> (built-in functions, |
| 68 | exceptions and <code>None</code>) and <tt class="module">__main__</tt>. The latter is used |
| 69 | to provide the local and global namespace for execution of the |
| 70 | complete program. |
| 71 | <a id='l2h-623' xml:id='l2h-623'></a> |
| 72 | |
| 73 | <P> |
| 74 | The syntax for a complete Python program is that for file input, |
| 75 | described in the next section. |
| 76 | |
| 77 | <P> |
| 78 | The interpreter may also be invoked in interactive mode; in this case, |
| 79 | it does not read and execute a complete program but reads and executes |
| 80 | one statement (possibly compound) at a time. The initial environment |
| 81 | is identical to that of a complete program; each statement is executed |
| 82 | in the namespace of <tt class="module">__main__</tt>. |
| 83 | <a id='l2h-624' xml:id='l2h-624'></a> |
| 84 | |
| 85 | <P> |
| 86 | Under <span class="Unix">Unix</span>, a complete program can be passed to the interpreter in |
| 87 | three forms: with the <b class="programopt">-c</b> <var>string</var> command line option, as a |
| 88 | file passed as the first command line argument, or as standard input. |
| 89 | If the file or standard input is a tty device, the interpreter enters |
| 90 | interactive mode; otherwise, it executes the file as a complete |
| 91 | program. |
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