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bpo-30969: Fix docs about the comparison in absence of __contains__ (GH-2761)

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(cherry picked from commit 2f5b9dcc0a)

Co-authored-by: Antti Haapala <antti@haapala.name>
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Miss Islington (bot) 2019-05-30 13:41:06 -07:00 • committed by GitHub
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Doc/reference/expressions.rst
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@ -1568,14 +1568,15 @@ y`` returns ``True`` if ``y.__contains__(x)`` returns a true value, and
``False`` otherwise.
For user-defined classes which do not define :meth:`__contains__` but do define
:meth:`__iter__`, ``x in y`` is ``True`` if some value ``z`` with ``x == z`` is
produced while iterating over ``y``. If an exception is raised during the
iteration, it is as if :keyword:`in` raised that exception.
:meth:`__iter__`, ``x in y`` is ``True`` if some value ``z``, for which the
expression ``x is z or x == z`` is true, is produced while iterating over ``y``.
If an exception is raised during the iteration, it is as if :keyword:`in` raised
that exception.
Lastly, the old-style iteration protocol is tried: if a class defines
:meth:`__getitem__`, ``x in y`` is ``True`` if and only if there is a non-negative
integer index *i* such that ``x == y[i]``, and all lower integer indices do not
raise :exc:`IndexError` exception. (If any other exception is raised, it is as
integer index *i* such that ``x is y[i] or x == y[i]``, and no lower integer index
raises the :exc:`IndexError` exception. (If any other exception is raised, it is as
if :keyword:`in` raised that exception).
.. index::