def listify(val, return_type=tuple):
    """
    Examples:
        >>> listify('abc', return_type=list)
        ['abc']
        >>> listify(None)
        ()
        >>> listify(False)
        (False,)
        >>> listify(('a', 'b', 'c'), return_type=list)
        ['a', 'b', 'c']
    """
    # TODO: flatlistify((1, 2, 3), 4, (5, 6, 7))
    if val is None:
        return return_type()
    elif isiterable(val):
        return return_type(val)
    else:
        return return_type((val, ))