kbe/src/lib/python/Doc/reference/toplevel_components.rst
.. _top-level:
Top-level components
.. index:: single: interpreter
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.
.. _programs:
.. index:: single: program
.. index:: module: sys module: main module: builtins
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 :mod:sys (various system services), :mod:builtins (built-in
functions, exceptions and None) and :mod:__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.
.. index:: single: interactive mode module: main
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
:mod:__main__.
.. index:: single: UNIX single: Windows single: command line single: standard input
A complete program can be passed to the interpreter
in three forms: with the :option:-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.
.. _file-input:
All input read from non-interactive files has the same form:
.. productionlist::
file_input: (NEWLINE | statement)*
This syntax is used in the following situations:
when parsing a complete Python program (from a file or from a string);
when parsing a module;
when parsing a string passed to the :func:exec function;
.. _interactive:
Input in interactive mode is parsed using the following grammar:
.. productionlist::
interactive_input: [stmt_list] NEWLINE | compound_stmt NEWLINE
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.
.. _expression-input:
.. index:: single: input .. index:: builtin: eval
:func:eval is used for expression input. It ignores leading whitespace. The
string argument to :func:eval must have the following form:
.. productionlist::
eval_input: expression_list NEWLINE*