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6.20.2.5 Print a version number

Similar to the brief usage string, `optparse` can also print a version string for your program. You have to supply the string, as the version argument to `OptionParser`:

    parser = OptionParser(usage="%prog [-f] [-q]", version="%prog 1.0")

version can contain anything you like; `%prog` is expanded in version just as with usage. When you supply it, `optparse` automatically adds a --version option to your parser. If it encounters this option on the command line, it expands your version string (by replacing `%prog`), prints it to stdout, and exits.

For example, if your script is called /usr/bin/foo, a user might do:

    $ /usr/bin/foo --version
    foo 1.0