6.21.2 Tutorial

6.21.2 Tutorial

While optparse is quite flexible and powerful, it's also straightforward to use in most cases. This section covers the code patterns that are common to any optparse-based program.

First, you need to import the OptionParser class; then, early in the main program, create an OptionParser instance:

from optparse import OptionParser
[...]
parser = OptionParser()

Then you can start defining options. The basic syntax is:

parser.add_option(opt_str, ...,
                  attr=value, ...)

Each option has one or more option strings, such as "-f" or "-file", and several option attributes that tell optparse what to expect and what to do when it encounters that option on the command line.

Typically, each option will have one short option string and one long option string, e.g.:

parser.add_option("-f", "--file", ...)

You're free to define as many short option strings and as many long option strings as you like (including zero), as long as there is at least one option string overall.

The option strings passed to add_option() are effectively labels for the option defined by that call. For brevity, we will frequently refer to encountering an option on the command line; in reality, optparse encounters option strings and looks up options from them.

Once all of your options are defined, instruct optparse to parse your program's command line:

(options, args) = parser.parse_args()

(If you like, you can pass a custom argument list to parse_args(), but that's rarely necessary: by default it uses sys.argv[1:].)

parse_args() returns two values:

• options, an object containing values for all of your options--e.g. if "-file" takes a single string argument, then options.file will be the filename supplied by the user, or None if the user did not supply that option

• args, the list of positional arguments leftover after parsing options

This tutorial section only covers the four most important option attributes: action, type, dest (destination), and help. Of these, action is the most fundamental.

---

Python Library Reference

Previous: 6.21.1.3 What are positional Up: 6.21 optparse Next: 6.21.2.1 Understanding option actions

---

Release 2.4.4c1, documentation updated on 11 October 2006.