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6.20.4.2 How callbacks are called

All callbacks are called as follows:

    func(option, opt, value, parser, *args, **kwargs)

where

option
  is the `Option` instance that's calling the callback.

opt
  is the option string seen on the command-line that's triggering the callback. (If an abbreviated long option was used, opt will be the full, canonical option string--for example, if the user puts --foo on the command-line as an abbreviation for --foobar, then opt will be --foobar.)

value
  is the argument to this option seen on the command-line. `optparse` will only expect an argument if type is set; the type of value will be the type implied by the option's type (see 6.20.3, ``Option types''). If type for this option is `None` (no argument expected), then value will be `None`. If "`nargs > 1`", value will be a tuple of values of the appropriate type.

parser
  is the `OptionParser` instance driving the whole thing, mainly useful because you can access some other interesting data through it, as instance attributes:

  parser.rargs
    the current remaining argument list, i.e. with opt (and value, if any) removed, and only the arguments following them still there. Feel free to modify `parser.rargs`, e.g. by consuming more arguments.

  parser.largs
    the current set of leftover arguments, i.e. arguments that have been processed but have not been consumed as options (or arguments to options). Feel free to modify `parser.largs` e.g. by adding more arguments to it.

  parser.values
    the object where option values are by default stored. This is useful because it lets callbacks use the same mechanism as the rest of `optparse` for storing option values; you don't need to mess around with globals or closures. You can also access the value(s) of any options already encountered on the command-line.

args
  is a tuple of arbitrary positional arguments supplied via the callback_args option attribute.

kwargs
  is a dictionary of arbitrary keyword arguments supplied via callback_kwargs.

Since args and kwargs are optional (they are only passed if you supply callback_args and/or callback_kwargs when you define your callback option), the minimal callback function is:

    def my_callback (option, opt, value, parser):
        pass