我在运行

set FLASK_APP=hello_fask.py
flask run

提示

 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
Usage: flask run [OPTIONS]

Error: Could not locate a Flask application. You did not provide the "FLASK_APP" environment
 variable, and a "wsgi.py" or "app.py" module was not found in the current directory.

无法直接运行，必须调用

if __name__ == '__main__':
    from gevent import pywsgi

    server = pywsgi.WSGIServer(('0.0.0.0', 5000), app)
    server.serve_forever()

才能运行成功，