cached_property in slotted classes doesn't work if overridden in child class #1333
Description
With attrs 24.2.0 and 23.2.0, if you use cached_property and try to override it in a child, and access the parent value, you get an AttributeError. We ran into this in our code when converting some classes to use slots.
I see there was support added in 24.2.0 for
Allow super() calls in slotted cached properties
But attrs still doesn't support "super() calls of overridden cached_property's in slotted classes":
from functools import cached_property
import attrs
@attrs.define(slots=True)
class Parent:
@cached_property
def name(self) -> str:
return "Alice"
@attrs.define(slots=True)
class Child(Parent):
@cached_property
def name(self) -> str:
return f"Bob (son of {super().name})"
p = Parent()
print(p.name) # prints Alice
c = Child()
print(c.name) # error:Traceback (most recent call last):
File "foo.py", line 23, in <module>
print(c.name)
^^^^^^
File "<attrs generated getattr __main__.Child>", line 6, in __getattr__
File "foo.py", line 18, in name
return f"Bob (son of {super().name})"
^^^^^^^^^^^^
AttributeError: 'Child' object has no attribute 'name'
Workarounds:
- disable slots
- don't use cached_property
- don't override the method
Elaboration:
I see the special handling is described in the docs and I see in the code that it generates a special __getattr__ that sets the generated value in the slot after being called. Perhaps when constructing a class, attrs should also walk the MRO for cached_propertys and handle any overridden cached_property methods — perhaps create some sort of namespaced/name-mangled properties for the parent.