template = """class %(typename)s(tuple):
    '%(typename)s(%(argtxt)s)' 

    __slots__ = () 

    _fields = %(field_names)r 

    def __new__(_cls, %(argtxt)s):
        'Create new instance of %(typename)s(%(argtxt)s)'
        return _tuple.__new__(_cls, (%(argtxt)s)) 

    ..."""
Use of exec and eval in Python