This issue tracker has been migrated to GitHub, and is currently read-only.
For more information, see the GitHub FAQs in the Python's Developer Guide.

classification
Title: AttributeError from @property inadvertantly flows into __getattr__
Type: behavior Stage:
Components: Versions: Python 3.11, Python 3.10, Python 3.9
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: AlexWaygood, koreno
Priority: normal Keywords:

Created on 2021-12-05 11:02 by koreno, last changed 2022-04-11 14:59 by admin.

Messages (1)
msg407701 - (view) Author: Ofer Koren (koreno) Date: 2021-12-05 11:02
There's For quite a long time I've been seeing this bug:

>>> class A():

...     @property
...     def foo(self):
...         return self.bar  # <---- this is where it all starts ('bar' isn't found)
... 
...     def __getattr__(self, attr):
...         raise AttributeError(attr)  # <--- let's pretend our getattr couldn't find the attr


>>> A().foo


Traceback (most recent call last):
  File "t.py", line 13, in <module>
    A().foo
  File "t.py", line 10, in __getattr__
    raise AttributeError(attr)
AttributeError: foo


So an AttributeError spawned by `self.bar` caused us to "fallback" on __getattr__ with attr='foo', leading the naive code there to produce a very confusing error message.


My workaround was to use a @safe_property decorator, one that catches AttributeError exceptions and converts them to RuntimeErrors instead, so that they don't flow into the unsuspecting __getattr__.
I believe python should adopt this behavior into the built-in property decorator, perhaps with a more appropriate exception type.
History
Date User Action Args
2022-04-11 14:59:53adminsetgithub: 90143
2021-12-12 19:45:16AlexWaygoodsetversions: - Python 3.6, Python 3.7, Python 3.8
2021-12-05 11:35:40AlexWaygoodsetnosy: + AlexWaygood
2021-12-05 11:02:26korenocreate