使用 Flask-Script 时，导入 Manager 时出现错误。
我已经安装了 pip Flask 和 Flask-Script。我该如何解决？
管理文件
from flask_script import Manager
from main import app
manager = Manager(app)
@manager.command
def hello():
print ("hello")
if __name__ == "__main__":
manager.run()
主文件
from flask import Flask
app = Flask(__name__)
错误
from flask_script import Manager
from main import app
manager = Manager(app)
@manager.command
def hello():
print ("hello")
if __name__ == "__main__":
manager.run()