/Doc/library/constants.rst
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- Built-in Constants
- ==================
- A small number of constants live in the built-in namespace. They are:
- .. data:: False
- The false value of the :class:`bool` type.
- .. versionadded:: 2.3
- .. data:: True
- The true value of the :class:`bool` type.
- .. versionadded:: 2.3
- .. 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.
- .. versionchanged:: 2.4
- Assignments to ``None`` are illegal and raise a :exc:`SyntaxError`.
- .. 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
- Special value used in conjunction with extended slicing syntax.
- .. XXX Someone who understands extended slicing should fill in here.
- .. data:: __debug__
- This constant is true if Python was not started with an :option:`-O` option.
- Assignments to :const:`__debug__` are illegal and raise a :exc:`SyntaxError`.
- See also the :keyword:`assert` statement.
- Constants added by the :mod:`site` module
- -----------------------------------------
- The :mod:`site` module (which is imported automatically during startup, except
- if the :option:`-S` command-line option is given) adds several constants to the
- built-in namespace. They are useful for the interactive interpreter shell and
- should not be used in programs.
- .. data:: quit([code=None])
- exit([code=None])
- Objects that when printed, print a message like "Use quit() or Ctrl-D
- (i.e. EOF) to exit", and when called, raise :exc:`SystemExit` with the
- specified exit code, and when .
- .. data:: copyright
- license
- credits
- Objects that when printed, print a message like "Type license() to see the
- full license text", and when called, display the corresponding text in a
- pager-like fashion (one screen at a time).