def version_argument(parser, core=core):
    """Version information command line option, allows override of the core
    class instance where required.

    `parser`
        Instance of ArgumentParser.
    `core`
        Package core instance.
    """
    version_kwargs = {'action': 'version', 'version': str('%(prog)s (' +
        core.version + ')')}
    parser.add_argument('-v', '--version', **version_kwargs)
