Python中的appen和extend

append和extend有什么区别?

append:

x = [1, 2, 3]
x.append([4, 5])
print (x)

输出:[1, 2, 3, [4, 5]]

extend:

x = [1, 2, 3]
x.extend([4, 5])
print (x)

输出:[1, 2, 3, 4, 5]