What is Flask?
Flask is a web framework written in Python. A web framework is a program that listens for HTTP requests and runs Python functions to generate responses.
Static vs. Dynamic
Without Flask — the old, static web. Every page is a complete .html file stored on a server. Ask for a page, get a file. Ask 1000 times, get the same file 1000 times.
With Flask — the dynamic web. Every page is generated by a Python function, in response to each request. The page can be different every time.
Flask is a tool designed to make this process "easy."
It will not seem easy. Flask is complex. But learning how to use this complex tool is much easier than doing all of the Flask functions by hand — which is what you were doing last week when you generated HTML from a Python script.
The five-line Hello World
Here is the smallest possible Flask application:
from flask import Flask
app = Flask(__name__)
@app.route("/")
def index():
return "<h1>Hello, World!</h1>"That's it. Five lines, and you have a web server. The rest of this section breaks down each line.