Python Syntax doubt

Hey, I have been using the Pymt library and they have this convention to referring their widgets:

from pymt import *

# create a slider from 0.-1.
sl = MTXYSlider()

@s开发者_如何学JAVAl.event
def on_value_change(x, y):
    print 'Slider value change', x, y

runTouchApp(sl)

what's with the "@"? What does it signify in Python?Thanks.

It signifies a decorator

basically it is a function that takes another function as an argument . if is a way python implements a Decorator Pattern.

the equivalent code would be

sl.event(on_value_change(x, y))