"getopt" --- 用於命令列選項的 C 風格剖析器
******************************************

**原始碼：**Lib/getopt.py

備註:

  This module is considered feature complete. A more declarative and
  extensible alternative to this API is provided in the "optparse"
  module. Further functional enhancements for command line parameter
  processing are provided either as third party modules on PyPI, or
  else as features in the "argparse" module.

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

This module helps scripts to parse the command line arguments in
"sys.argv". It supports the same conventions as the Unix "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.

Users who are unfamiliar with the Unix "getopt()" function should
consider using the "argparse" module instead. Users who are familiar
with the Unix "getopt()" function, but would like to get equivalent
behavior while writing less code and getting better help and error
messages should consider using the "optparse" module. See 選擇一個命令
列參數剖析函式庫 for additional details.

這個模組提供兩個函式和一個例外：

getopt.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 ("':'")
   and options that accept an optional argument followed by two colons
   ("'::'"); i.e., the same format that Unix "getopt()" uses.

   備註:

     Unlike GNU "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
   ("'='"). Long options which accept an optional argument should be
   followed by an equal sign and question mark ("'=?'"). 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 "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.

   在 3.14 版的變更: Optional arguments are supported.

getopt.gnu_getopt(args, shortopts, longopts=[])

   This function works like "getopt()", except that GNU style scanning
   mode is used by default. This means that option and non-option
   arguments may be intermixed. The "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.

   If the first character of the option string is "'-'", non-option
   arguments that are followed by options are added to the list of
   option-and-value pairs as a pair that has "None" as its first
   element and the list of non-option arguments as its second element.
   The second element of the "gnu_getopt()" result is a list of
   program arguments after the last option.

   在 3.14 版的變更: Support for returning intermixed options and non-
   option arguments in order.

exception getopt.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 "msg" and "opt" give the error message and related
   option; if there is no specific option to which the exception
   relates, "opt" is an empty string.

exception getopt.error

   為了向後相容性而設的 "GetoptError" 別名。

一個僅使用 Unix 風格選項的範例：

   >>> 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']

使用長選項名稱同樣容易：

   >>> 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']

Optional arguments should be specified explicitly:

   >>> s = '-Con -C --color=off --color a1 a2'
   >>> args = s.split()
   >>> args
   ['-Con', '-C', '--color=off', '--color', 'a1', 'a2']
   >>> optlist, args = getopt.getopt(args, 'C::', ['color=?'])
   >>> optlist
   [('-C', 'on'), ('-C', ''), ('--color', 'off'), ('--color', '')]
   >>> args
   ['a1', 'a2']

The order of options and non-option arguments can be preserved:

   >>> s = 'a1 -x a2 a3 a4 --long a5 a6'
   >>> args = s.split()
   >>> args
   ['a1', '-x', 'a2', 'a3', 'a4', '--long', 'a5', 'a6']
   >>> optlist, args = getopt.gnu_getopt(args, '-x:', ['long='])
   >>> optlist
   [(None, ['a1']), ('-x', 'a2'), (None, ['a3', 'a4']), ('--long', 'a5')]
   >>> args
   ['a6']

在腳本中，典型的用法如下：

   import getopt, sys

   def main():
       try:
           opts, args = getopt.getopt(sys.argv[1:], "ho:v", ["help", "output="])
       except getopt.GetoptError as err:
           # 印出幫助訊息並退出：
           print(err)  # 會印出像是 "option -a not recognized" 的訊息
           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"
       process(args, output=output, verbose=verbose)

   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
"optparse" module:

   import optparse

   if __name__ == '__main__':
       parser = optparse.OptionParser()
       parser.add_option('-o', '--output')
       parser.add_option('-v', dest='verbose', action='store_true')
       opts, args = parser.parse_args()
       process(args, output=opts.output, verbose=opts.verbose)

A roughly equivalent command line interface for this case can also be
produced by using the "argparse" module:

   import argparse

   if __name__ == '__main__':
       parser = argparse.ArgumentParser()
       parser.add_argument('-o', '--output')
       parser.add_argument('-v', dest='verbose', action='store_true')
       parser.add_argument('rest', nargs='*')
       args = parser.parse_args()
       process(args.rest, output=args.output, verbose=args.verbose)

參見 選擇一個命令列參數剖析函式庫 以瞭解這段程式碼的 "argparse" 版本與
"optparse"（以及 "getopt"）版本在行為上的差異。

也參考:

  "optparse" 模組
     宣告式命令列選項剖析。

  "argparse" 模組
     More opinionated command line option and argument parsing
     library.
