what‘s wrong

现在我看不出来我的问题在哪里！

原题是要返回传入list or tuple的奇数位的元素，但是我用下面的方式会报错，在append那里目前，当下闭门造车，实在没有看到问题在哪里

tup = [11,12,13,14,15,16,17,18,19]
lis = []
for i in range(0,len(tup),2):
    print tup[i]
    lis1 = lis.append(tup[i])
print lis1

执行结果：

Python 2.7.11 (v2.7.11:6d1b6a68f775, Dec  5 2015, 20:40:30) [MSC v.1500 64 bit (AMD64)] on win32
Type "copyright", "credits" or "license()" for more information.
>>>
======================= RESTART: C:/Python27/error.py =======================
11
13
15
17
19
None
>>> 

没有试过Python3

但是在Linux下面直接运行也是一样的错误；

但是感觉逻辑没有问题，或者说至少暂时我没有看到问题

tup = [11,12,13,14,15,16,17,18,19]
lis = []
for i in range(0,len(tup),2):
    a = tup[i]
    print lis
    print type(a)
    print a
    lis1 = lis.append(a)
    print lis1
    print lis

酱紫后lis 是我想要的，但是为啥lis1却是None呢？

Python 2.7.11 (v2.7.11:6d1b6a68f775, Dec  5 2015, 20:40:30) [MSC v.1500 64 bit (AMD64)] on win32
Type "copyright", "credits" or "license()" for more information.
>>>
======================= RESTART: C:/Python27/error.py =======================
[]
<type ‘int‘>
11
None
[11]
[11]
<type ‘int‘>
13
None
[11, 13]
[11, 13]
<type ‘int‘>
15
None
[11, 13, 15]
[11, 13, 15]
<type ‘int‘>
17
None
[11, 13, 15, 17]
[11, 13, 15, 17]
<type ‘int‘>
19
None
[11, 13, 15, 17, 19]
>>>