刚学python，用flask_script为什么会报这个错，求提点提点

问题遇到的现象和发生背景

使用flask_script
manager.run()的时候报错

问题相关代码，请勿粘贴截图

Traceback (most recent call last):
  File "manager.py", line 16, in <module>
    sys.exit(main())
  File "manager.py", line 9, in main
    manager.run()
  File "E:\Python\lib\site-packages\flask_script\__init__.py", line 412, in run
    argv = list(text_type(arg) for arg in sys.argv)
  File "E:\Python\lib\site-packages\flask_script\__init__.py", line 412, in <genexpr>
    argv = list(text_type(arg) for arg in sys.argv)
NameError: name 'text_type' is not defined

下面是我的代码：manager.py

from application import app,manager
from flask_script import Server

##web server
manager.add_command( "runserver", Server( host='0.0.0.0',port=3306,use_debugger = True ,use_reloader = True) )


def main():
    manager.run()


if __name__ == '__main__':
    try:
        import sys

        sys.exit(main())
    except Exception as e:
        import traceback

        traceback.print_exc()

下面是我的代码：application.py

# -*- coding: utf-8 -*-
from flask import Flask
from flask_script import Manager
from flask_sqlalchemy import SQLAlchemy
import os


class Application( Flask ):
    def __init__(self,import_name):
        super( Application,self ).__init__( import_name )
        self.config.from_pyfile( 'config/base_setting.py' )
        if "ops_config" in os.environ:
            self.config.from_pyfile( 'config/%s_setting.py'%os.environ['ops_config'] )

        db.init_app( self )


db = SQLAlchemy()
app = Application( __name__ )
manager = Manager( app )

text_type变量没有定义