mirror of https://github.com/python/cpython
52 lines
1.3 KiB
ReStructuredText
52 lines
1.3 KiB
ReStructuredText
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Built-in Constants
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==================
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A small number of constants live in the built-in namespace. They are:
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.. note::
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:data:`None`, :data:`False`, :data:`True` and :data:`__debug__` cannot be
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reassigned, so they can be considered "true" constants.
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.. XXX False, True, None are keywords too
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.. data:: False
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The false value of the :class:`bool` type.
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.. data:: True
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The true value of the :class:`bool` type.
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.. data:: None
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The sole value of :attr:`types.NoneType`. ``None`` is frequently used to
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represent the absence of a value, as when default arguments are not passed to a
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function.
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.. data:: NotImplemented
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Special value which can be returned by the "rich comparison" special methods
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(:meth:`__eq__`, :meth:`__lt__`, and friends), to indicate that the comparison
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is not implemented with respect to the other type.
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.. data:: Ellipsis
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The same as ``...``. Special value used mostly in conjunction with extended
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slicing syntax for user-defined container data types, as in ::
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val = container[1:5, 7:10, ...]
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.. data:: __debug__
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A boolean value that is :data:`True` if Python was not started with the
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``-O`` command line option. Its value is used indirectly by the
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:keyword:`assert` statement, but it can also be used directly in code.
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