Return the user name to use when creating git objects or exit
    program.

    Parameters
    ----------
    args: parser.parse_args()

    Returns
    -------
    user: `string`
        git user name

def lookup_user(args):
    """Return the user name to use when creating git objects or exit
    program.

    Parameters
    ----------
    args: parser.parse_args()

    Returns
    -------
    user: `string`
        git user name
    """
    user = args.user
    if user is None:
        user = gitusername()

    if user is None:
        raise RuntimeError(textwrap.dedent("""\
            unable to determine a git user name
            Specify --user option\
        """))

    debug("user name is {user}".format(user=user))

    return user