14.3 optparse -- More powerful command line option parser

# 14.3 `optparse` -- More powerful command line option parser

New in version 2.3.

`optparse` is a more convenient, flexible, and powerful library for parsing command-line options than `getopt`. `optparse` uses a more declarative style of command-line parsing: you create an instance of `OptionParser`, populate it with options, and parse the command line. `optparse` allows users to specify options in the conventional GNU/POSIX syntax, and additionally generates usage and help messages for you.

Here's an example of using `optparse` in a simple script:

    from optparse import OptionParser
    [...]
    parser = OptionParser()
    parser.add_option("-f", "--file", dest="filename",
                      help="write report to FILE", metavar="FILE")
    parser.add_option("-q", "--quiet",
                      action="store_false", dest="verbose", default=True,
                      help="don't print status messages to stdout")

    (options, args) = parser.parse_args()

With these few lines of code, users of your script can now do the ``usual thing'' on the command-line, for example:

    <yourscript> --file=outfile -q

As it parses the command line, `optparse` sets attributes of the `options` object returned by `parse_args()` based on user-supplied command-line values. When `parse_args()` returns from parsing this command line, `options.filename` will be `"outfile"` and `options.verbose` will be `False`. `optparse` supports both long and short options, allows short options to be merged together, and allows options to be associated with their arguments in a variety of ways. Thus, the following command lines are all equivalent to the above example:

    <yourscript> -f outfile --quiet
    <yourscript> --quiet --file outfile
    <yourscript> -q -foutfile
    <yourscript> -qfoutfile

Additionally, users can run one of

    <yourscript> -h
    <yourscript> --help

and `optparse` will print out a brief summary of your script's options:

    usage: <yourscript> [options]

    options:
      -h, --help            show this help message and exit
      -f FILE, --file=FILE  write report to FILE
      -q, --quiet           don't print status messages to stdout

where the value of yourscript is determined at runtime (normally from `sys.argv[0]`).