无法从其他目录导入python类

这里我有以下目录结构,

src/models/UserModel.py
src/resources/UserResources.py

和 UserModel.py 包含

from datetime import datetime
from run import db
from passlib.hash import pbkdf2_sha256 as sha256
from sqlalchemy.orm import relationship
from sqlalchemy import Column, Integer, ForeignKey
from flask import jsonify


class UserModel(db.Model):
    __tablename__ = 'users'

    id            = db.Column(db.Integer, primary_key = True)
    username      = db.Column(db.String(120), unique = True, nullable = False)
    password      = db.Column(db.String(120), nullable = False)
    user_role     = db.Column(db.String(10), nullable = False)
    access_token  = db.Column(db.String(120), unique = True, nullable = True)
    refresh_token = db.Column(db.String(120), unique = True, nullable = True)

    def save_to_db(self):
        db.session.add(self)
        db.session.commit()

和 UserResources.py 文件导入 UserModel 这样地 from models import UserModel

即使models目录中有 __init__.py 文件,它引发以下错误 ImportError: cannot import name 'UserModel' from 'models'

我做错什么了?