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

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Merged
JelleZijlstra merged 9 commits into from
Dec 21, 2022
Merged

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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Add workaround example
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@slateny
slateny committed Dec 10, 2022
commit 9f22bd7fcb1442d9180bafd2d1d40837c89a1813
14 changes: 12 additions & 2 deletions Doc/library/weakref.rst
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Expand Up @@ -172,15 +172,25 @@ See :ref:`__slots__ documentation <slots>` for details.
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
>>> 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 = {}

A workaround would be to remove the key prior to reassignment::

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Outdated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

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

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