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bpo-37913: document that __length_hint__ can return NotImplemented (GH-15383)

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Jeroen Demeyer 2019-09-10 16:01:13 +02:00 • committed by Steve Dower
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Doc/reference/datamodel.rst
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@ -2155,8 +2155,10 @@ through the container; for mappings, :meth:`__iter__` should be the same as
Called to implement :func:`operator.length_hint`. Should return an estimated Called to implement :func:`operator.length_hint`. Should return an estimated
length for the object (which may be greater or less than the actual length). length for the object (which may be greater or less than the actual length).
The length must be an integer ``>=`` 0. This method is purely an The length must be an integer ``>=`` 0. The return value may also be
optimization and is never required for correctness. *NotImplemented*, which is treated the same as if the ``__length_hint__``
method didn't exist at all. This method is purely an optimization and is
never required for correctness.
.. versionadded:: 3.4 .. versionadded:: 3.4