# 2.4 Built-in Constants

A small number of constants live in the built-in namespace. They are:

`False`
  The false value of the `bool` type. New in version 2.3.

`True`
  The true value of the `bool` type. New in version 2.3.

`None`
  The sole value of ``types`.NoneType`. `None` is frequently used to represent the absence of a value, as when default arguments are not passed to a function.

`NotImplemented`
  Special value which can be returned by the ``rich comparison'' special methods (`__eq__()`, `__lt__()`, and friends), to indicate that the comparison is not implemented with respect to the other type.

`Ellipsis`
  Special value used in conjunction with extended slicing syntax.