A small number of constants live in the built-in namespace. They are:
The false value of thebool type. Assignments toFalseare illegal and raise aSyntaxError.
The true value of thebool type. Assignments toTrueare illegal and raise aSyntaxError.
The sole value of the typeNoneType.None is frequently used torepresent the absence of a value, as when default arguments are not passed to afunction. Assignments toNone are illegal and raise aSyntaxError.
Special value which can be returned by the “rich comparison” special methods(__eq__(),__lt__(), and friends), to indicate that the comparisonis not implemented with respect to the other type.
The same as.... Special value used mostly in conjunction with extendedslicing syntax for user-defined container data types.
This constant is true if Python was not started with an-O option.See also theassert statement.
Note
The namesNone,False,True and__debug__cannot be reassigned (assignments to them, even as an attribute name, raiseSyntaxError), so they can be considered “true” constants.
Thesite module (which is imported automatically during startup, exceptif the-S command-line option is given) adds several constants to thebuilt-in namespace. They are useful for the interactive interpreter shell andshould not be used in programs.
Objects that when printed, print a message like “Use quit() or Ctrl-D(i.e. EOF) to exit”, and when called, raiseSystemExit with thespecified exit code.
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