__hash__ implemented inBaseModel subclass no longer called with functools.cache

[d-chambers]

Initial Checks

• I confirm that I'm using Pydantic V2

Description

In V1 I was able to overwrite the default __hash__ method such that functools.cache would work for models that have mutable parameters (numpy array, which had its write flag set to False). This no longer works in V2.

Related issues: #2423, #1880

Example Code

from functools import _lru_cache_wrapper, cached_property, cache

import numpy as np
from pydantic import ConfigDict, BaseModel


class MyBaseModel(BaseModel):
    """A base model with sensible configurations."""
    model_config = ConfigDict(
        ignored_types=(cached_property, _lru_cache_wrapper),
        frozen=True,
        arbitrary_types_allowed=True,
    )

    def __hash__(self):
        return hash(id(self))


class MySubClass(MyBaseModel):
    ar: np.ndarray

    @cached_property
    def cached_prop(self):
        return self.ar.shape

    @cache
    def cached_method(self):
        return self.ar.size


my_instance = MySubClass(ar=np.ones(10))

my_instance.cached_prop

my_instance.cached_method()

Python, Pydantic & OS Version

pydantic version: 2.0.3
        pydantic-core version: 2.3.0 release build profile
                 install path: /home/derrick/anaconda3/envs/dascore/lib/python3.10/site-packages/pydantic
               python version: 3.10.11 | packaged by conda-forge | (main, May 10 2023, 18:58:44) [GCC 11.3.0]
                     platform: Linux-5.15.0-76-generic-x86_64-with-glibc2.31
     optional deps. installed: ['typing-extensions']

Selected Assignee: @adriangb

[d-chambers]

I should say, this raises this exception:

  File ".../lib/python3.10/site-packages/pydantic/_internal/_model_construction.py", line 122, in hash_func
    return hash(self.__class__) + hash(tuple(self.__dict__.values()))
TypeError: unhashable type: 'numpy.ndarray'

[dmontagu]

I think I see a fix for this; I think a short-term work-around may be to do __hash__ = MyBaseModel.__hash__ in the definition of MySubClass, but I'll work on fixing so this isn't necessary.