Difference between @app and app in flask

Question

I'm new in python. And I can't seem to figure why sometimes in tutorials and examples you see the "@" sign before a variable

the basic flask app look like so:

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello ():
     return "Hello World!"

if __name__ == "__main__":
     app.run()

So how come they need to use the @ sign and when can I use it?

Answer 1

They are called decorators. Please refer to: https://www.python.org/dev/peps/pep-0318/