flask 'hello world' not working

Question

I copy pasted the flask's 'hello world' app from their website and am trying to run it. I get an error message in Chrome saying

Internal Server Error

The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.

Here is the 'hello world' app straight from flasks website

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello World!'

if __name__ == '__main__':
    app.debug = True
    app.run()

What I have tried:

-temporarily disabling Avast!

-disabling windows firewall

-ensuring that the flask module is installed

This was working a couple days ago actually...

Answer 1

I don't know why but when I change

app.run()

to

app.run(port=4996)

it starts working. No idea why the default port is throwing an error. Oh well.

Answer 2

from flask import Flask

app = Flask(__name__)


@app.route('/')
def index():
    return 'Hello World'


if __name__ == '__name__':
    app.run()

app.run(port=5000)