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gh-91081: Add note on WeakKeyDictionary behavior when deleting a replaced entry #91499

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merged 9 commits into from
Dec 21, 2022
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gh-91081: Add note on WeakKeyDictionary behavior when deleting a replaced entry #91499

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ea0f7ba
Add note about new key not replacing existing key for weakref
slateny Apr 13, 2022
5961498
Add extra sentence to correct misunderstanding of issue
slateny Apr 13, 2022
4ccddc5
Add missing "the"
slateny Apr 13, 2022
3c1413d
Add specific example
slateny Apr 27, 2022
c2f649f
Make example runnable
slateny Apr 27, 2022
c4ac22d
Add weakref. for dict example
slateny Apr 27, 2022
69b3231
Remove one newline
slateny Dec 10, 2022
9f22bd7
Add workaround example
slateny Dec 10, 2022
e17e69f
Use del over pop()
slateny Dec 21, 2022
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15 changes: 15 additions & 0 deletions Doc/library/weakref.rst
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Expand Up @@ -167,6 +167,21 @@ See :ref:`__slots__ documentation <slots>` for details.
application without adding attributes to those objects. This can be especially
useful with objects that override attribute accesses.

Note that when a key with equal value to an existing key (but not equal identity)
is inserted into the dictionary, it replaces the value but does not replace the
existing key. Due to this, when the reference to the original key is deleted, it
also deletes the entry in the dictionary::

>>> class T(str):
... pass
...
>>> k1, k2 = T(), T()
>>> d = weakref.WeakKeyDictionary()
>>> d[k1] = 1 # d = {k1: 1}
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>>> d[k2] = 2 # d = {k1: 2}
>>> del k1 # d = {}


.. versionchanged:: 3.9
Added support for ``|`` and ``|=`` operators, specified in :pep:`584`.

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