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.