AttributeError：'NoneType'对象没有属性'_instantiate_plugins'（无法导入create_engine）

Question

import os

from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session, sessionmaker

engine=create_engine(os.getenv("DATABASE_URL"))
db = scoped_session(sessionmaker(bind=engine))

def main():
    flights = db.execute("SELECT origin, destination, duration FROM flights").fetchall()
    for flight in flights:
        print(f"{flight.origin} to {flight.destination}, {flight.duration} minutes.")

if __name__ == "__main__":
    main()

追踪（最近通话）：文件“ list.py”，第6行，在engine = create_engine（os.getenv（“ DATABASE_URL”））文件“ C：\ Users \ Aakash \ AppData \ Local \ Programs \ Python \ Python38-32 \ lib \ site-packages \ sqlalchemy \ engine__init __。py”，create_engine中的第479行返回strategy.create（* args，** kwargs）创建文件“ C：\ Users \ Aakash \ AppData \ Local \ Programs \ Python \ Python38-32 \ lib \ site-packages \ sqlalchemy \ engine \ strategies.py”，行56插件= u._instantiate_plugins（kwargs）AttributeError：“ NoneType”对象没有属性“ _instantiate_plugins”

如果将我的代码更改为：

The Problem and the traceback is in the picture.