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14.3.2.7 Printing a version string

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")

`"%prog"` is expanded just like it is in `usage`. Apart from that, `version` can contain anything you like. 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`:

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