:mod:`getopt` --- C-style parser for command line options

.. module:: getopt
 :synopsis: Portable parser for command line options; support both short and
 long option names.

Source code: :source:`Lib/getopt.py`

This module helps scripts to parse the command line arguments in sys.argv. It supports the same conventions as the Unix :c:func:`getopt` function (including the special meanings of arguments of the form '-' and '--'). Long options similar to those supported by GNU software may be used as well via an optional third argument.

This module provides two functions and an exception:

.. function:: getopt(args, shortopts, longopts=[])

 Parses command line options and parameter list. *args* is the argument list to
 be parsed, without the leading reference to the running program. Typically, this
 means ``sys.argv[1:]``. *shortopts* is the string of option letters that the
 script wants to recognize, with options that require an argument followed by a
 colon (``':'``; i.e., the same format that Unix :c:func:`getopt` uses).

 .. note::

 Unlike GNU :c:func:`getopt`, after a non-option argument, all further
 arguments are considered also non-options. This is similar to the way
 non-GNU Unix systems work.

 *longopts*, if specified, must be a list of strings with the names of the
 long options which should be supported. The leading ``'--'`` characters
 should not be included in the option name. Long options which require an
 argument should be followed by an equal sign (``'='``). Optional arguments
 are not supported. To accept only long options, *shortopts* should be an
 empty string. Long options on the command line can be recognized so long as
 they provide a prefix of the option name that matches exactly one of the
 accepted options. For example, if *longopts* is ``['foo', 'frob']``, the
 option ``--fo`` will match as ``--foo``, but ``--f`` will
 not match uniquely, so :exc:`GetoptError` will be raised.

 The return value consists of two elements: the first is a list of ``(option,
 value)`` pairs; the second is the list of program arguments left after the
 option list was stripped (this is a trailing slice of *args*). Each
 option-and-value pair returned has the option as its first element, prefixed
 with a hyphen for short options (e.g., ``'-x'``) or two hyphens for long
 options (e.g., ``'--long-option'``), and the option argument as its
 second element, or an empty string if the option has no argument. The
 options occur in the list in the same order in which they were found, thus
 allowing multiple occurrences. Long and short options may be mixed.

.. function:: gnu_getopt(args, shortopts, longopts=[])

 This function works like :func:`getopt`, except that GNU style scanning mode is
 used by default. This means that option and non-option arguments may be
 intermixed. The :func:`getopt` function stops processing options as soon as a
 non-option argument is encountered.

 If the first character of the option string is ``'+'``, or if the environment
 variable :envvar:`POSIXLY_CORRECT` is set, then option processing stops as
 soon as a non-option argument is encountered.

.. exception:: GetoptError

 This is raised when an unrecognized option is found in the argument list or when
 an option requiring an argument is given none. The argument to the exception is
 a string indicating the cause of the error. For long options, an argument given
 to an option which does not require one will also cause this exception to be
 raised. The attributes :attr:`msg` and :attr:`opt` give the error message and
 related option; if there is no specific option to which the exception relates,
 :attr:`opt` is an empty string.

.. exception:: error

 Alias for :exc:`GetoptError`; for backward compatibility.

An example using only Unix style options:

>>> import getopt
>>> args = '-a -b -cfoo -d bar a1 a2'.split()
>>> args
['-a', '-b', '-cfoo', '-d', 'bar', 'a1', 'a2']
>>> optlist, args = getopt.getopt(args, 'abc:d:')
>>> optlist
[('-a', ''), ('-b', ''), ('-c', 'foo'), ('-d', 'bar')]
>>> args
['a1', 'a2']

Using long option names is equally easy:

>>> s = '--condition=foo --testing --output-file abc.def -x a1 a2'
>>> args = s.split()
>>> args
['--condition=foo', '--testing', '--output-file', 'abc.def', '-x', 'a1', 'a2']
>>> optlist, args = getopt.getopt(args, 'x', [
... 'condition=', 'output-file=', 'testing'])
>>> optlist
[('--condition', 'foo'), ('--testing', ''), ('--output-file', 'abc.def'), ('-x', '')]
>>> args
['a1', 'a2']

In a script, typical usage is something like this:

import getopt, sys

def main():
 try:
 opts, args = getopt.getopt(sys.argv[1:], "ho:v", ["help", "output="])
 except getopt.GetoptError as err:
 # print help information and exit:
 print(err) # will print something like "option -a not recognized"
 usage()
 sys.exit(2)
 output = None
 verbose = False
 for o, a in opts:
 if o == "-v":
 verbose = True
 elif o in ("-h", "--help"):
 usage()
 sys.exit()
 elif o in ("-o", "--output"):
 output = a
 else:
 assert False, "unhandled option"
 # ...

if __name__ == "__main__":
 main()

Note that an equivalent command line interface could be produced with less code and more informative help and error messages by using the :mod:`argparse` module:

import argparse

if __name__ == '__main__':
 parser = argparse.ArgumentParser()
 parser.add_argument('-o', '--output')
 parser.add_argument('-v', dest='verbose', action='store_true')
 args = parser.parse_args()
 # ... do something with args.output ...
 # ... do something with args.verbose ..

.. seealso::

 Module :mod:`argparse`
 Alternative command line option and argument parsing library.

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