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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
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
optimization and is never required for correctness.
The length must be an integer ``>=`` 0. The return value may also be
*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