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(python2.1-ref.info)Complete Python programs

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Complete Python programs
========================

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 `sys' (various
system services), `__builtin__' (built-in functions, exceptions and
`None') and `__main__'.  The latter is used to provide the local and
global namespace for execution of the complete program.

The syntax for a complete Python program is that for file input,
described in the next section.

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 `__main__'.

Under {UNIX}, a complete program can be passed to the interpreter in
three forms: with the `-c' STRING 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.