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107 lines
3.1 KiB
ReStructuredText
107 lines
3.1 KiB
ReStructuredText
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.. _top-level:
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********************
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Top-level components
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********************
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.. index:: single: interpreter
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The Python interpreter can get its input from a number of sources: from a script
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passed to it as standard input or as program argument, typed in interactively,
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from a module source file, etc. This chapter gives the syntax used in these
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cases.
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.. _programs:
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Complete Python programs
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========================
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.. index:: single: program
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.. index::
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pair: module; sys
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pair: module; __main__
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pair: module; builtins
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While a language specification need not prescribe how the language interpreter
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is invoked, it is useful to have a notion of a complete Python program. A
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complete Python program is executed in a minimally initialized environment: all
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built-in and standard modules are available, but none have been initialized,
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except for :mod:`sys` (various system services), :mod:`builtins` (built-in
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functions, exceptions and ``None``) and :mod:`__main__`. The latter is used to
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provide the local and global namespace for execution of the complete program.
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The syntax for a complete Python program is that for file input, described in
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the next section.
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.. index::
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single: interactive mode
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pair: module; __main__
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The interpreter may also be invoked in interactive mode; in this case, it does
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not read and execute a complete program but reads and executes one statement
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(possibly compound) at a time. The initial environment is identical to that of
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a complete program; each statement is executed in the namespace of
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:mod:`__main__`.
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.. index::
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single: UNIX
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single: Windows
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single: command line
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single: standard input
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A complete program can be passed to the interpreter
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in three forms: with the :option:`-c` *string* command line option, as a file
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passed as the first command line argument, or as standard input. If the file
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or standard input is a tty device, the interpreter enters interactive mode;
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otherwise, it executes the file as a complete program.
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.. _file-input:
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File input
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==========
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All input read from non-interactive files has the same form:
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.. productionlist:: python-grammar
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file_input: (NEWLINE | `statement`)*
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This syntax is used in the following situations:
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* when parsing a complete Python program (from a file or from a string);
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* when parsing a module;
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* when parsing a string passed to the :func:`exec` function;
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.. _interactive:
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Interactive input
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=================
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Input in interactive mode is parsed using the following grammar:
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.. productionlist:: python-grammar
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interactive_input: [`stmt_list`] NEWLINE | `compound_stmt` NEWLINE
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Note that a (top-level) compound statement must be followed by a blank line in
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interactive mode; this is needed to help the parser detect the end of the input.
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.. _expression-input:
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Expression input
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================
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.. index:: single: input
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.. index:: pair: built-in function; eval
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:func:`eval` is used for expression input. It ignores leading whitespace. The
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string argument to :func:`eval` must have the following form:
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.. productionlist:: python-grammar
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eval_input: `expression_list` NEWLINE*
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