14.3.2.2 The store action

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14.3.2.2 The store action

The most common option action is `store`, which tells `optparse` to take the next argument (or the remainder of the current argument), ensure that it is of the correct type, and store it to your chosen destination.

For example:

    parser.add_option("-f", "--file",
                      action="store", type="string", dest="filename")

Now let's make up a fake command line and ask `optparse` to parse it:

    args = ["-f", "foo.txt"]
    (options, args) = parser.parse_args(args)

When `optparse` sees the option string `"-f"`, it consumes the next argument, `"foo.txt"`, and stores it in `options.filename`. So, after this call to `parse_args()`, `options.filename` is `"foo.txt"`.

Some other option types supported by `optparse` are `int` and `float`. Here's an option that expects an integer argument:

    parser.add_option("-n", type="int", dest="num")

Note that this option has no long option string, which is perfectly acceptable. Also, there's no explicit action, since the default is `store`.

Let's parse another fake command-line. This time, we'll jam the option argument right up against the option: since `"-n42"` (one argument) is equivalent to `"-n 42"` (two arguments), the code

    (options, args) = parser.parse_args(["-n42"])
    print options.num

will print `"42"`.

If you don't specify a type, `optparse` assumes `string`. Combined with the fact that the default action is `store`, that means our first example can be a lot shorter:

    parser.add_option("-f", "--file", dest="filename")

If you don't supply a destination, `optparse` figures out a sensible default from the option strings: if the first long option string is `"-foo-bar"`, then the default destination is `foo_bar`. If there are no long option strings, `optparse` looks at the first short option string: the default destination for `"-f"` is `f`.

`optparse` also includes built-in `long` and `complex` types. Adding types is covered in section 14.3.5, Extending `optparse`.