Python inheritance - Interfaces/classes

Question

from langchain.schema import BaseMemory

class ChatMemory(BaseMemory):
   def __init__(self, user_id: UUID, type: str):
    self.user_id = user_id
    self.type = type

   # implemented abstract methods

class AnotherMem(ChatMemory):
    def __init__(self, user_id: UUID, type: str):
        super().__init__(user_id, type)

This seems simple enough - but I get an error: ValueError: "AnotherMem" object has no field "user_id". What am I doing wrong?

Note that BaseMemory is an interface.

Answer 1

It looks like BaseMemory from langchain is defined as a pydantic model, which has strict rules for defining instance attributes. Instead of using a constructor method, use the standard pydantic syntax of declaring expected instance attributes on the child class.

import uuid
from langchain.schema import BaseMemory


class ChatMemory(BaseMemory):
    user_id: uuid.UUID
    type: str

    ...

class AnotherMem(ChatMemory):
    pass


print(AnotherMem(user_id=uuid.uuid4(), type="foo").user_id)

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