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      1 :mod:`getopt` --- C-style parser for command line options
      2 =========================================================
      3 
      4 .. module:: getopt
      5    :synopsis: Portable parser for command line options; support both short and long option
      6               names.
      7 
      8 **Source code:** :source:`Lib/getopt.py`
      9 
     10 --------------
     11 
     12 .. note::
     13 
     14    The :mod:`getopt` module is a parser for command line options whose API is
     15    designed to be familiar to users of the C :c:func:`getopt` function. Users who
     16    are unfamiliar with the C :c:func:`getopt` function or who would like to write
     17    less code and get better help and error messages should consider using the
     18    :mod:`argparse` module instead.
     19 
     20 This module helps scripts to parse the command line arguments in ``sys.argv``.
     21 It supports the same conventions as the Unix :c:func:`getopt` function (including
     22 the special meanings of arguments of the form '``-``' and '``--``').  Long
     23 options similar to those supported by GNU software may be used as well via an
     24 optional third argument.
     25 
     26 This module provides two functions and an
     27 exception:
     28 
     29 
     30 .. function:: getopt(args, options[, long_options])
     31 
     32    Parses command line options and parameter list.  *args* is the argument list to
     33    be parsed, without the leading reference to the running program. Typically, this
     34    means ``sys.argv[1:]``. *options* is the string of option letters that the
     35    script wants to recognize, with options that require an argument followed by a
     36    colon (``':'``; i.e., the same format that Unix :c:func:`getopt` uses).
     37 
     38    .. note::
     39 
     40       Unlike GNU :c:func:`getopt`, after a non-option argument, all further
     41       arguments are considered also non-options. This is similar to the way
     42       non-GNU Unix systems work.
     43 
     44    *long_options*, if specified, must be a list of strings with the names of the
     45    long options which should be supported.  The leading ``'--'``
     46    characters should not be included in the option name.  Long options which
     47    require an argument should be followed by an equal sign (``'='``).  Optional
     48    arguments are not supported.  To accept only long options, *options* should
     49    be an empty string.  Long options on the command line can be recognized so
     50    long as they provide a prefix of the option name that matches exactly one of
     51    the accepted options.  For example, if *long_options* is ``['foo', 'frob']``,
     52    the option ``--fo`` will match as ``--foo``, but ``--f``
     53    will not match uniquely, so :exc:`GetoptError` will be raised.
     54 
     55    The return value consists of two elements: the first is a list of ``(option,
     56    value)`` pairs; the second is the list of program arguments left after the
     57    option list was stripped (this is a trailing slice of *args*).  Each
     58    option-and-value pair returned has the option as its first element, prefixed
     59    with a hyphen for short options (e.g., ``'-x'``) or two hyphens for long
     60    options (e.g., ``'--long-option'``), and the option argument as its
     61    second element, or an empty string if the option has no argument.  The
     62    options occur in the list in the same order in which they were found, thus
     63    allowing multiple occurrences.  Long and short options may be mixed.
     64 
     65 
     66 .. function:: gnu_getopt(args, options[, long_options])
     67 
     68    This function works like :func:`getopt`, except that GNU style scanning mode is
     69    used by default. This means that option and non-option arguments may be
     70    intermixed. The :func:`getopt` function stops processing options as soon as a
     71    non-option argument is encountered.
     72 
     73    If the first character of the option string is ``'+'``, or if the environment
     74    variable :envvar:`POSIXLY_CORRECT` is set, then option processing stops as
     75    soon as a non-option argument is encountered.
     76 
     77    .. versionadded:: 2.3
     78 
     79 
     80 .. exception:: GetoptError
     81 
     82    This is raised when an unrecognized option is found in the argument list or when
     83    an option requiring an argument is given none. The argument to the exception is
     84    a string indicating the cause of the error.  For long options, an argument given
     85    to an option which does not require one will also cause this exception to be
     86    raised.  The attributes :attr:`msg` and :attr:`opt` give the error message and
     87    related option; if there is no specific option to which the exception relates,
     88    :attr:`opt` is an empty string.
     89 
     90    .. versionchanged:: 1.6
     91       Introduced :exc:`GetoptError` as a synonym for :exc:`error`.
     92 
     93 
     94 .. exception:: error
     95 
     96    Alias for :exc:`GetoptError`; for backward compatibility.
     97 
     98 An example using only Unix style options:
     99 
    100    >>> import getopt
    101    >>> args = '-a -b -cfoo -d bar a1 a2'.split()
    102    >>> args
    103    ['-a', '-b', '-cfoo', '-d', 'bar', 'a1', 'a2']
    104    >>> optlist, args = getopt.getopt(args, 'abc:d:')
    105    >>> optlist
    106    [('-a', ''), ('-b', ''), ('-c', 'foo'), ('-d', 'bar')]
    107    >>> args
    108    ['a1', 'a2']
    109 
    110 Using long option names is equally easy:
    111 
    112    >>> s = '--condition=foo --testing --output-file abc.def -x a1 a2'
    113    >>> args = s.split()
    114    >>> args
    115    ['--condition=foo', '--testing', '--output-file', 'abc.def', '-x', 'a1', 'a2']
    116    >>> optlist, args = getopt.getopt(args, 'x', [
    117    ...     'condition=', 'output-file=', 'testing'])
    118    >>> optlist
    119    [('--condition', 'foo'), ('--testing', ''), ('--output-file', 'abc.def'), ('-x', '')]
    120    >>> args
    121    ['a1', 'a2']
    122 
    123 In a script, typical usage is something like this::
    124 
    125    import getopt, sys
    126 
    127    def main():
    128        try:
    129            opts, args = getopt.getopt(sys.argv[1:], "ho:v", ["help", "output="])
    130        except getopt.GetoptError as err:
    131            # print help information and exit:
    132            print str(err)  # will print something like "option -a not recognized"
    133            usage()
    134            sys.exit(2)
    135        output = None
    136        verbose = False
    137        for o, a in opts:
    138            if o == "-v":
    139                verbose = True
    140            elif o in ("-h", "--help"):
    141                usage()
    142                sys.exit()
    143            elif o in ("-o", "--output"):
    144                output = a
    145            else:
    146                assert False, "unhandled option"
    147        # ...
    148 
    149    if __name__ == "__main__":
    150        main()
    151 
    152 Note that an equivalent command line interface could be produced with less code
    153 and more informative help and error messages by using the :mod:`argparse` module::
    154 
    155    import argparse
    156 
    157    if __name__ == '__main__':
    158        parser = argparse.ArgumentParser()
    159        parser.add_argument('-o', '--output')
    160        parser.add_argument('-v', dest='verbose', action='store_true')
    161        args = parser.parse_args()
    162        # ... do something with args.output ...
    163        # ... do something with args.verbose ..
    164 
    165 .. seealso::
    166 
    167    Module :mod:`argparse`
    168       Alternative command line option and argument parsing library.
    169 
    170