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bpo-30969: Fix docs about the comparison in absence of __contains__ #2761

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Merged
merged 4 commits into from
May 30, 2019
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bpo-30969: Fix docs about the comparison in absence of __contains__ #2761

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6d411c6
Fix the eq check that is used in absence of `__contains__`
ztane Jul 19, 2017
29abde0
lowercase the true, as it need not be `True`.
ztane Jul 19, 2017
511406d
Add the missing space here.
ztane Jul 19, 2017
b4f285f
Fix trailing whitespace
csabella May 30, 2019
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11 changes: 6 additions & 5 deletions Doc/reference/expressions.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -1443,14 +1443,15 @@ 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::
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