有两种类型的回调函数:
blocking callbacks (also kNown as synchronous callbacks or just callbacks)
deferred callbacks (also kNown as asynchronous callbacks)
def my_callback(input):
print "function my_callback was called with %s input" % (input,)
def caller(input,func):
func(input)
for i in range(5):
caller(i,my_callback)