append()向列表尾部添加一个新的元素，只接受一个参数
extend()只接受一个列表作为参数，将参数中的每个元素都添加到原列表
append()用法示例：
>> mylist = [1,2,0,‘abc‘]
>> mylist [1, 2, 0, ‘abc‘]
>> mylist.append(4)
>> mylist [1, 2, 0, ‘abc‘, 4]
>> mylist.append(‘haha‘)
>> mylist [1, 2, 0, ‘abc‘, 4, ‘haha‘]
extend()用法示例:
>> mylist [1, 2, 0, ‘abc‘, 4, ‘haha‘]
>> mylist.extend([‘lulu‘])
>> mylist [1, 2, 0, ‘abc‘, 4, ‘haha‘, ‘lulu‘]
>> mylist.extend([‘123123‘,‘lalalala‘])
>> mylist [1, 2, 0, ‘abc‘, 4, ‘haha‘, ‘lulu‘, ‘123123‘, ‘lalalala‘]
>> mylist.extend([111111,222])
>> mylist [1, 2, 0, ‘abc‘, 4, ‘haha‘, ‘lulu‘, ‘123123‘, ‘lalalala‘, 111111, 222]