python - what does the "@" operator does in this code (python 3.7.5). I cant seem to understand

Question

I am fairly new to coding and i dont know what most of this code does but I am trying to get my head around it i just wanted to know what does "@" mean or rather what it does. Thanks in advance.

import pyglet
import pymunk
from pymunk.pyglet_util import DrawOptions

comprimento = 1280
altura=720
window = pyglet.window.Window(comprimento,altura, "Plano inclinado", resizable=False)
options= DrawOptions()

space = pymunk.Space()
space.gravity = 0 , -9.8

body = pymunk.Body(1,1666)
body.position  = 640,700
poly = pymunk.Poly.create_box(body)

space.add(body,poly)

@window.event
def on_draw():
    window.clear()
    space.debug_draw(options)

def update(dt):
    space.step(dt)

if __name__ == "__main__":
    pyglet.clock.schedule_interval(update,0.01)
    pyglet.app.run()```