8.1 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.
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