被route()装饰器所装饰的functions()必须有返回值

from flask import Flaskapp = Flask(__name__)@app.route('/')def hello_world():    'Hello World!'                    # 没有关键字returnif __name__ == '__main__':    app.run()

TypeError: The view function did not return a valid response. The function either returned None or ended without a return statement.

为什么要构建URL

pass

from werkzeug import secure_filename 报错

from werkzeug.utils import secure_filename