New submission from Daniel Romberg <dan...@romberg.io>:
The copy operation is not safe to use during iteration. The following test case
raises a "RuntimeError: dictionary changed size during iteration":
import weakref
class Class:
pass
def TEST_weakValue():
d = weakref.WeakValueDictionary()
a = Class()
b = Class()
d["a"] = a
d["b"] = b
e = d.copy()
for key in e:
a = None
c = e.copy()
TEST_weakValue()
This is related to https://bugs.python.org/issue35615 where I commented as
well, but I couldn't find a way to reopen this issue, which is why I open this
one.
We experience a lot fewer crashes in weakref than before
https://bugs.python.org/issue35615 had been fixed, however, there are recursive
situations in which copy() is invoked while iterating the WeakValueDictionary
(e.g., in our case it is a signal/slot implementation where the slots are
stored in a WeakValueDictionary). _commit_removals(), which is called at the
beginning of the copy operation, might change the dictionary if there are items
that are to be removed. If there is an ongoing iteration, the corresponding
RuntimeError is raised.
I haven't thought that through entirely, but I wonder whether the copy (and
also deepcopy) operation could just blindly copy everything without "committing
removals". After the copy, both instances would do their _commit_removals on
their own upon access.
----------
components: Library (Lib)
messages: 385779
nosy: djromberg
priority: normal
severity: normal
status: open
title: copying WeakValueDictionary is not iteration safe
type: crash
versions: Python 3.10, Python 3.6, Python 3.7, Python 3.8, Python 3.9
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue43041>
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