Can't define variable in pydantic init function

I want to define a BaseDomain model that inherits from pydantic BaseModel like below

class BaseDomain(BaseModel):

    def __init__(self, **kwargs):
        self.__exceptions = []

    def add_error(self, exception: GeneralException):
        self.__exceptions.append(exception)

but I get this error when I use Product model that inherits from BaseDomain

ValueError: "Product" object has no field "_BaseDomain__exceptions"

Because you have overidden pydantic's init method that is executed when a class that inherits from BaseModel is created. you should call super()

def __init__(self, **kwargs):
    super().__init__(**kwargs)
    self.__exceptions = []

EDIT

It seems that pydantic throws that error because it validates __exceptions as an input and throws an error because it isn't defined in the classes annotations

Try this:

from typing import List, Any

class BaseDomain(BaseModel):
    __exceptions:List[Any] = []

    def __init__(self, **kwargs):
        super().__init__(**kwargs)