Why Sweating the Details Matter: Flask, port 5000, localhost, Safari and macOS
Pop quiz: Suppose you are developing a Flask app. Flask uses port 5000 as its default port. Now suppose that you have your Flask app running on macOS on port 5000. You're testing in Safari1 and you enter this URL into the address bar: http://localhost:5000. Question: What will happen? Answer: You won't get your Flask app. Instead, you'll likely get a whole lot of nothing, which can be very confusing because of two overlapping factors. It turns out, 5000 is the default port for AirPlay. You might
