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

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Steve Dower 2019-09-10 15:31:26 +01:00 committed by GitHub
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Doc/reference/datamodel.rst
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@ -2155,7 +2155,9 @@ 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
The length must be an integer ``>=`` 0. The return value may also be
:const:`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