IsInstance does not work for Pydantic BaseModels

[StefanBRas]

It seems like IsInstance will never be equal to a pydantic model:

from dirty_equals import IsInstance
from pydantic import BaseModel

class A(BaseModel): pass

print(A() == IsInstance(A)) # False
print(A() == IsInstance[A]) # False

class B: pass

print(B() == IsInstance(B)) # True
print(B() == IsInstance[B]) # True

Interestingly enough it works perfectly with IsPartialDict:

from dirty_equals import IsPartialDict, IsNegativeInt
from pydantic import BaseModel

class C(BaseModel):
    a: int
    b: str

print(C(a=-1,b="a") ==  IsPartialDict(a=IsNegativeInt)) # True
print(C(a=-1,b="a") ==  IsPartialDict(a=IsNegativeInt, b=1)) # False

Maybe it's also nice to document that IsPartialDict works with pydantic models without having to call model_instance.dict()?

Tested with dirty-equals version 0.50 and pydantic versions 1.9.0 and 1.10.7.

[StefanBRas]

Ah, I see now that pydantic does

def __eq__(self, other: Any) -> bool:
    if isinstance(other, BaseModel):
        return self.dict() == other.dict()
    else:
        return self.dict() == other

So it will do the dict equality check instead.

So in the other order, it works:

print(IsInstance(A) == A()) # True
print(IsInstance[A] == A()) # True

I guess it can't really be changed, unless you were like the maintainer of pydantic or something (😉) and I'd doubt they would ever do that because It would break a lot of peoples code.

Feel free to close the issue, I'll leave it up so you can decide if there should be something in the documentation about this.

[samuelcolvin]

That's changing in V2, also the __eq__ logic shouldn't affect the IsInstance() check.

[alexmojaki]

That's changing in V2

Indeed, A() == IsInstance(A) is True with pydantic V2.

also the __eq__ logic shouldn't affect the IsInstance() check.

Not sure what you mean here, but it makes sense that the old BaseModel.__eq__ prevented IsInstance from working since it doesn't go through the usual NotImplemented pattern. It evaluates self.dict() == other which leads to IsInstance checking if a dict is an instance of a model class. So I think it's impossible to fix this for pydantic v1 without changes to pydantic v1 or some monkeypatching here.