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====== 4. Built-in Constants ======
Created Sunday 02 December 2012

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.

Changed in version 2.4: Assignments to None are illegal and raise a SyntaxError.

===== 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.

===== __debug__ =====
This constant is true if Python was __not started with an -O option__. See also the assert statement.

Note The names None and __debug__ cannot be reassigned (assignments to them, even as an attribute name, raise SyntaxError), so they can be considered “true” constants.
Changed in version 2.7: Assignments to __debug__ as an attribute became illegal.

===== 4.1. Constants added by the site module =====
The site module (which is __imported automatically during startup__, except if the -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.

===== 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 SystemExit with the specified exit code.

==== 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).

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