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[3.6] bpo-15718: Document the upper bound constrain on the __len__ re… #1259

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Apr 23, 2017
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[3.6] bpo-15718: Document the upper bound constrain on the __len__ re… #1259

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9 changes: 9 additions & 0 deletions Doc/reference/datamodel.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -2011,6 +2011,14 @@ through the container; for mappings, :meth:`__iter__` should be the same as
:meth:`__bool__` method and whose :meth:`__len__` method returns zero is
considered to be false in a Boolean context.

.. impl-detail::

In CPython, the length is required to be at most :attr:`sys.maxsize`.
If the length is larger than :attr:`!sys.maxsize` some features (such as
:func:`len`) may raise :exc:`OverflowError`. To prevent raising
:exc:`!OverflowError` by truth value testing, an object must define a
:meth:`__bool__` method.


.. method:: object.__length_hint__(self)

Expand All @@ -2021,6 +2029,7 @@ through the container; for mappings, :meth:`__iter__` should be the same as

.. versionadded:: 3.4


.. note::

Slicing is done exclusively with the following three methods. A call like ::
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