Upgrading optparse code

Originally, the argparse module had attempted to maintain compatibility with optparse. However, optparse was difficult to extend transparently, particularly with the changes required to support nargs= specifiers and better usage messages. When most everything in optparse had either been copy-pasted over or monkey-patched, it no longer seemed practical to try to maintain the backwards compatibility.

The argparse module improves on the optparse module in a number of ways including:

• Handling positional arguments.

• Supporting subcommands.

• Allowing alternative option prefixes like + and /.

• Handling zero-or-more and one-or-more style arguments.

• Producing more informative usage messages.

• Providing a much simpler interface for custom type and action.

A partial upgrade path from optparse to argparse:

• Replace all optparse.OptionParser.add_option() calls with ArgumentParser.add_argument() calls.

• Replace (options, args) = parser.parse_args() with args = parser.parse_args() and add additional ArgumentParser.add_argument() calls for the positional arguments. Keep in mind that what was previously called options, now in the argparse context is called args.

• Replace optparse.OptionParser.disable_interspersed_args() by using parse_intermixed_args() instead of parse_args().

• Replace callback actions and the callback_* keyword arguments with type or action arguments.

• Replace string names for type keyword arguments with the corresponding type objects (e.g. int, float, complex, etc).

• Replace optparse.Values with Namespace and optparse.OptionError and optparse.OptionValueError with ArgumentError.

• Replace strings with implicit arguments such as %default or %prog with the standard Python syntax to use dictionaries to format strings, that is, %(default)s and %(prog)s.

• Replace the OptionParser constructor version argument with a call to parser.add_argument('--version', action='version', version='<the version>').