6.21.3.7 Parsing arguments

The whole point of creating and populating an OptionParser is to call its parse_args() method:

(options, args) = parser.parse_args(args=None, options=None)

where the input parameters are

args: the list of arguments to process (sys.argv[1:] by default)
options: object to store option arguments in (a new instance of optparse.Values by default)

and the return values are

options: the same object as was passed in as options, or the new optparse.Values instance created by optparse
args: the leftover positional arguments after all options have been processed

The most common usage is to supply neither keyword argument. If you supply a values object, it will be repeatedly modified with a setattr() call for every option argument written to an option destination, and finally returned by parse_args().

If parse_args() encounters any errors in the argument list, it calls the OptionParser's error() method with an appropriate end-user error message. This ultimately terminates your process with an exit status of 2 (the traditional Unix exit status for command-line errors).

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