New submission from Ryan Heisler :
In the documentation for `weakref.finalize`
(https://docs.python.org/3.9/library/weakref.html#weakref.finalize), it says:
"Note It is important to ensure that func, args and kwargs do not own any
references to obj, either directly or indirectly, since otherwise obj will
never be garbage collected. In particular, func should not be a bound method of
obj."
However, at the bottom of the document, in the section called "Comparing
finalizers with __del__() methods"
(https://docs.python.org/3.8/library/weakref.html#comparing-finalizers-with-del-methods),
the following code is part of an example of how to use `weakref.finalize`:
class TempDir:
def __init__(self):
self.name = tempfile.mkdtemp()
self._finalizer = weakref.finalize(self, shutil.rmtree, self.name)
I believe this code violates the rule that func, args, and kwargs should not
have a reference to obj. In the example, obj is the instance of TempDir, and
one of the arguments to finalize's callback is an attribute of the same
instance of TempDir.
I do not know how to fix this example code. I found it while trying to figure
out how to use `weakref.finalize`.
--
assignee: docs@python
components: Documentation
messages: 385155
nosy: docs@python, ryan.a.heisler
priority: normal
severity: normal
status: open
title: weakref.finalize documentation contradicts itself RE: finalizer callback
or args referencing object
versions: Python 3.10, Python 3.6, Python 3.7, Python 3.8, Python 3.9
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