install flask and run HelloWorld webapp

(venv) lindas-MacBook-Air:hello linda$ pip3 install flask

(venv) lindas-MacBook-Air:hello linda$ export FLASK_APP=hello.py

(venv) lindas-MacBook-Air:hello linda$ export FLASK_DEBUG=1

(venv) lindas-MacBook-Air:hello linda$ flask run

(venv) lindas-MacBook-Air:hello linda$ cat hello.py

from flask import Flask

app = Flask(__name__)

@app.route('/')

def hello():

return "Hello World!"

(venv) lindas-MacBook-Air:hello linda$ flask run

* Serving Flask app "hello.py" (lazy loading)

* Environment: production

WARNING: This is a development server. Do not use it in a production deployment.

Use a production WSGI server instead.

* Debug mode: on

* Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

* Restarting with stat

* Debugger is active!

* Debugger PIN: 337-750-709

if you add below two lines into hello.py:

if __name__ == "__main__":

app.run()

you can start app with: python3 hello.py directly!