Built-in Constants ================== A small number of constants live in the built-in namespace. They are: .. XXX False, True, None are keywords too .. data:: False The false value of the :class:`bool` type. .. data:: True The true value of the :class:`bool` type. .. data:: None The sole value of :attr:`types.NoneType`. ``None`` is frequently used to represent the absence of a value, as when default arguments are not passed to a function. .. data:: NotImplemented Special value which can be returned by the "rich comparison" special methods (:meth:`__eq__`, :meth:`__lt__`, and friends), to indicate that the comparison is not implemented with respect to the other type. .. data:: Ellipsis The same as ``...``. Special value used mostly in conjunction with extended slicing syntax for user-defined container data types, as in :: val = container[1:5, 7:10, ...]