SQLAlchemy question

model_test.py

import sqlalchemy as sa
from sqlalchemy.orm import declarative_base, relationship

Base = declarative_base()


class A(Base):
    __tablename__ = 'A'
    id = sa.Column(sa.Integer, primary_key=True)

    def __repr__(self) -> str:
        return f'<A(id={self.id})>'


class B(Base):
    __tablename__ = 'B'
    id = sa.Column(sa.Integer, primary_key=True)
    a_id = sa.Column(sa.Integer, sa.ForeignKey(A.id))
    a = relationship(A, backref="bs")

    def __repr__(self) -> str:
        return f'<B(id={self.id}, a={self.a})>'


def check():
    try:
        A.bs
        print("A.bs ok")
    except AttributeError as e:
        print(e)


check()
A()
check()

output.txt

type object 'A' has no attribute 'bs'
A.bs ok