Python, model <> model, how to avoid circular import

Let's say that I have an pydantic (it could be any kind of) model that shold know how to convert itself to orm (it could be any kind of) model. To do so I have constructed mod_a.py:

from pydantic import BaseModel

from mod2mod.mod_b import DBUser

class User(BaseModel):

    name: str
    surname: str

    def to_orm(self) -> DBUser:
        return DBUser(
            full_name = f"{self.surname},{self.name}"
        )

I would also like my orm model to be able to convert itself to pydantic model, so my mod_b.py is:

from sqlalchemy.orm import declarative_base
from sqlalchemy import Column, Integer, String
from mod_a import User

Base = declarative_base()

class DBUser(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    full_name = Column(String)

    def to_pydantic(self) -> User:
        surname, name = self.full_name.split(',')
        User(
            name=name,
            surname=surname
        )

Idea is to be able to go from model to model at will like in mod2mod.py:

import pydantic
from mod_a import User
from mod_b import DBUser


user = User(name='John', surname='Doe')
orm_user = user.to_orm()

pydantic_user = orm_user.to_pydantic()

print(user)
print(pydantic_user)

Obviously this will not work because:

ImportError: cannot import name 'User' from partially initialized module 'mod_a' (most likely due to a circular import) (/mod2mod/mod_a.py)

How to solve this type of problem? Do I need another entity that will now how to do conversions between models and put current model methods there or there is some other design pattern?