Flaky comparison for models with cached properties in version < 2.6

[marcus-idealworks]

Initial Checks

• I confirm that I'm using Pydantic V2

Description

The comparison of two objects of a pydantic model with a cached property shows unexpected behavior. The __eq__ operator does not explicitly evaluate cached properties. Therefore, the objects are compared based on previous evaluations. If a cached property was previously evaluated for exactly one of the compared objects, __eq__ results in False.

Expected behavior: If the cached properties have not been evaluated before a call to __eq__, they are evaluated during the comparison.

The issue is already resolved on main due to the changes of BaseModel.__eq__ (

pydantic/pydantic/main.py

Line 863 in 420d8c2

def __eq__(self, other: Any) -> bool:

).

Example Code

from pydantic import BaseModel
from functools import cached_property


class M(BaseModel):
    a: int
    b: int

    @cached_property
    def c(self) -> int:
        return self.a + self.b


m0 = M(a=1, b=2)
m1 = M(a=1, b=2)
m0.c
assert m0 == m1 # failing

Python, Pydantic & OS Version

             pydantic version: 2.5.0
        pydantic-core version: 2.14.1
          pydantic-core build: profile=release pgo=true
                 install path: /home/**/.venv/lib/python3.11/site-packages/pydantic
               python version: 3.11.6 (main, Nov 14 2023, 09:36:21) [GCC 13.2.1 20230801]
                     platform: Linux-6.5.12-1-MANJARO-x86_64-with-glibc2.38
             related packages: typing_extensions-4.8.0 mypy-0.991

[sydney-runkle]

Hi @marcus-idealworks,

Thanks for reporting this. @alexmojaki and @QuentinSoubeyranAqemia worked hard to fix this in #7825. This fix will be released with 2.6.0. If you need the fix now, you can pull from main :)

Closing as a dupe of #7444