mirror of https://github.com/python/cpython
124 lines
3.3 KiB
ReStructuredText
124 lines
3.3 KiB
ReStructuredText
|
|
.. _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:
|
|
|
|
Complete Python programs
|
|
========================
|
|
|
|
.. index:: single: program
|
|
|
|
.. index::
|
|
module: sys
|
|
module: __main__
|
|
module: __builtin__
|
|
|
|
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:`__builtin__` (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: command line
|
|
single: standard input
|
|
|
|
Under Unix, 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:
|
|
|
|
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:
|
|
|
|
Interactive input
|
|
=================
|
|
|
|
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:
|
|
|
|
Expression input
|
|
================
|
|
|
|
.. index:: single: input
|
|
|
|
.. index:: builtin: eval
|
|
|
|
There are two forms of expression input. Both ignore leading whitespace. The
|
|
string argument to :func:`eval` must have the following form:
|
|
|
|
.. productionlist::
|
|
eval_input: `expression_list` NEWLINE*
|
|
|
|
.. index:: builtin: input
|
|
|
|
The input line read by :func:`input` must have the following form:
|
|
|
|
.. productionlist::
|
|
input_input: `expression_list` NEWLINE
|
|
|
|
.. index::
|
|
object: file
|
|
single: input; raw
|
|
single: readline() (file method)
|
|
|
|
Note: to read 'raw' input line without interpretation, you can use the the
|
|
:meth:`readline` method of file objects, including ``sys.stdin``.
|
|
|