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#6324: membership test tries iteration via __iter__.

This commit is contained in:
Georg Brandl 2009-10-22 15:00:06 +00:00
parent 6c14e587f5
commit 2eee1d4df1
2 changed files with 16 additions and 5 deletions
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12
Doc/reference/datamodel.rst
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@ -1888,12 +1888,16 @@ implemented as an iteration through a sequence. However, container objects can
supply the following special method with a more efficient implementation, which
also does not require the object be a sequence.
.. method:: object.__contains__(self, item)
Called to implement membership test operators. Should return true if *item* is
in *self*, false otherwise. For mapping objects, this should consider the keys
of the mapping rather than the values or the key-item pairs.
Called to implement membership test operators. Should return true if *item*
is in *self*, false otherwise. For mapping objects, this should consider the
keys of the mapping rather than the values or the key-item pairs.
For objects that don't define :meth:`__contains__`, the membership test first
tries iteration via :meth:`__iter__`, then the old sequence iteration
protocol via :meth:`__getitem__`, see :ref:`this section in the language
reference <membership-test-details>`.
.. _sequence-methods:

9
Doc/reference/expressions.rst
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@ -1068,6 +1068,8 @@ Comparison of objects of the same type depends on the type:
another one is made arbitrarily but consistently within one execution of a
program.
.. _membership-test-details:
The operators :keyword:`in` and :keyword:`not in` test for collection
membership. ``x in s`` evaluates to true if *x* is a member of the collection
*s*, and false otherwise. ``x not in s`` returns the negation of ``x in s``.
@ -1092,7 +1094,12 @@ string, so ``"" in "abc"`` will return ``True``.
For user-defined classes which define the :meth:`__contains__` method, ``x in
y`` is true if and only if ``y.__contains__(x)`` is true.
For user-defined classes which do not define :meth:`__contains__` and do define
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.
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