# optparse --- Parser for command line options — Tutorial

> While !optparse is quite flexible and powerful, it's also straightforward to use in most cases.

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## Knowledge

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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 OptionParser.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 ~OptionParser.parse_args, but that's rarely necessary: by default it uses sys.argv[1:].)

~OptionParser.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: ~Option.action, ~Option.type, ~Option.dest (destination), and ~Option.help. Of these, ~Option.action is the most fundamental.

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