[New-bugs-announce] [issue45064] Raising AttributeError in descriptor decorator causing searching attribute in __mro__

[Mateusz]

New submission from Mateusz <blooser at protonmail.com>:

A descriptor that is raising AttributeError in __get__() causes that the Python's interpreter continues searching for attributes in __mro__ calling __getattr__() function in inherited classes.

Let's take a look for example script with this bug.


class A1:
    def __getattr__(self, name):
        print("A1 visited")
        raise AttributeError(f"{self.__class__.__name__}: {name} not found.")

class A2(A1):
    def __getattr__(self, name):
        print("A2 visited")
        super().__getattr__(name)


class A3(A2):
    def __getattr__(self, name):
        print("A3 visited")
        super().__getattr__(name)


class B:
    def __init__(self, f):
        self.f = f

    def __get__(self, obj, objtype=None):
        raise AttributeError("Python bug?")

class C(A3):
    @B
    def test(self):
        return 25

B is a decorator attached to C.test() and it is throwing AttributeError. When c.test() is performed it starts for walking through C.__mro__ and calling __getattr__() function in objects.

>>> from bug import C
>>> c = C()
>>> c.test()
A3 visited
A2 visited
A1 visited
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/blooser/python-bug/bug.py", line 17, in __getattr__
    super().__getattr__(name)
  File "/home/blooser/python-bug/bug.py", line 11, in __getattr__
    super().__getattr__(name)
  File "/home/blooser/python-bug/bug.py", line 6, in __getattr__
    raise AttributeError(f"{self.__class__.__name__}: {name} not found.")
AttributeError: C: test not found.

Changing error in B.__get__() to NameError:

class B:
    def __init__(self, f):
        self.f = f

    def __get__(self, obj, objtype=None):
        raise NameError("Python bug?")

causes it omits C.__mro__.

>>> from bug import C
>>> c = C()
>>> c.test()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/blooser/python-bug/bug.py", line 26, in __get__
    raise NameError("Python bug?")
NameError: Python bug?

I'm thinking that it is expected behavior or is this a bug?

----------
components: Interpreter Core
files: bug.py
messages: 400743
nosy: blooser
priority: normal
severity: normal
status: open
title: Raising AttributeError in descriptor decorator causing searching attribute in __mro__
type: behavior
versions: Python 3.11
Added file: https://bugs.python.org/file50248/bug.py

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue45064>
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