:mod:`getopt` --- Parser for command line options

=================================================

.. module:: getopt

   :synopsis: Portable parser for command line options; support both short and long option

              names.

This module helps scripts to parse the command line arguments in ``sys.argv``.

It supports the same conventions as the Unix :cfunc:`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.

A more convenient, flexible, and powerful alternative is the

:mod:`optparse` module.

This module provides two functions and an

exception:

.. function:: getopt(args, options[, long_options])

   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:]``. *options* 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 :cfunc:`getopt` uses).

   .. note::

      Unlike GNU :cfunc:`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.

   *long_options*, 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 (``'='``).  To accept only long

   options, *options* 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 *long_options* is

   ``['foo', 'frob']``, the option :option:`--fo` will match as :option:`--foo`,

   but :option:`--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, options[, long_options])

   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 POSIXLY_CORRECT is set, then option processing stops as soon as a

   non-option argument is encountered.

   .. versionadded:: 2.3

.. 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.

   .. versionchanged:: 1.6

      Introduced :exc:`GetoptError` as a synonym for :exc:`error`.

.. 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, err:

           # print help information and exit:

           print str(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()

.. seealso::

   Module :mod:`optparse`

      More object-oriented command line option parsing.