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  ,   ˆl–Ým_JJh¥ ² ¸È®2ú˜´oÅ„t?_‡I|¥ŠèªÁÉ ?÷     :mod:`argparse` --- Parser for command-line options, arguments and sub-commands
===============================================================================

.. module:: argparse
   :synopsis: Command-line option and argument parsing library.
.. moduleauthor:: Steven Bethard <steven.bethard@gmail.com>
.. sectionauthor:: Steven Bethard <steven.bethard@gmail.com>

.. versionadded:: 2.7

**Source code:** :source:`Lib/argparse.py`

--------------

.. sidebar:: Tutorial

   This page contains the API reference information. For a more gentle
   introduction to Python command-line parsing, have a look at the
   :ref:`argparse tutorial <argparse-tutorial>`.

The :mod:`argparse` module makes it easy to write user-friendly command-line
interfaces. The program defines what arguments it requires, and :mod:`argparse`
will figure out how to parse those out of :data:`sys.argv`.  The :mod:`argparse`
module also automatically generates help and usage messages and issues errors
when users give the program invalid arguments.


Example
-------

The following code is a Python program that takes a list of integers and
produces either the sum or the max::

   import argparse

   parser = argparse.ArgumentParser(description='Process some integers.')
   parser.add_argument('integers', metavar='N', type=int, nargs='+',
                      help='an integer for the accumulator')
   parser.add_argument('--sum', dest='accumulate', action='store_const',
                      const=sum, default=max,
                      help='sum the integers (default: find the max)')

   args = parser.parse_args()
   print args.accumulate(args.integers)

Assuming the Python code above is saved into a file called ``prog.py``, it can
be run at the command line and provides useful help messages::

   $ prog.py -h
   usage: prog.py [-h] [--sum] N [N ...]

   Process some integers.

   positional arguments:
    N           an integer for the accumulator

   optional arguments:
    -h, --help  show this help message and exit
    --sum       sum the integers (default: find the max)

When run with the appropriate arguments, it prints either the sum or the max of
the command-line integers::

   $ prog.py 1 2 3 4
   4

   $ prog.py 1 2 3 4 --sum
   10

If invalid arguments are passed in, it will issue an error::

   $ prog.py a b c
   usage: prog.py [-h] [--sum] N [N ...]
   prog.py: error: argument N: invalid int value: 'a'

The following sections walk you through this example.


Creating a parser
^^^^^^^^^^^^^^^^^

The first step in using the :mod:`argparse` is creating an
:class:`ArgumentParser` object::

   >>> parser = argparse.ArgumentParser(description='Process some integers.')

The :class:`ArgumentParser` object will hold all the information necessary to
parse the command line into Python data types.


Adding arguments
^^^^^^^^^^^^^^^^

Filling an :class:`ArgumentParser` with information about program arguments is
done by making calls to the :meth:`~ArgumentParser.add_argument` method.
Generally, these calls tell the :class:`ArgumentParser` how to take the strings
on the command line and turn them into objects.  This information is stored and
used when :meth:`~ArgumentParser.parse_args` is called. For example::

   >>> parser.add_argument('integers', metavar='N', type=int, nargs='+',
   ...                     help='an integer for the accumulator')
   >>> parser.add_argument('--sum', dest='accumulate', action='store_const',
   ...                     const=sum, default=max,
   ...                     help='sum the integers (default: find the max)')

Later, calling :meth:`~ArgumentParser.parse_args` will return an object with
two attributes, ``integers`` and ``accumulate``.  The ``integers`` attribute
will be a list of one or more ints, and the ``accumulate`` attribute will be
either the :func:`sum` function, if ``--sum`` was specified at the command line,
or the :func:`max` function if it was not.


Parsing arguments
^^^^^^^^^^^^^^^^^

:class:`ArgumentParser` parses arguments through the
:meth:`~Ar