python之append和extend的区别

list.append(object) 向列表中添加一个对象object
list.extend(sequence) 把一个序列seq的内容添加到列表中

a = ['a','aa','aaa']
b = ['B','BB','BBB']
c = ['C','CC','CCC']
a.append(b)
print(a)  #['a', 'aa', 'aaa', ['B', 'BB', 'BBB']]
b.extend(c)
print(b)  #['B', 'BB', 'BBB', 'C', 'CC', 'CCC']