为什么一个可以翻转,一个是none

Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 22:22:05) [MSC v.1916 64 bit (AMD64)] on win32
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L1=[4,5,6,8]
L1.reverse()
print(L1)
[8, 6, 5, 4]
L1=[4,5,6,8].reverse()
print(L1)
None
L1=[4,5,6,8]
L1=[4,5,6,8].reverse()
print(L2)
Traceback (most recent call last):
File “<pyshell#7>”, line 1, in
print(L2)
NameError: name ‘L2’ is not defined
L1=[4,5,6,8]
L2=[4,5,6,8].reverse()
print(L2)
None

list.reverse() 无返回值 所以得到 None 。 只会改变 list 的值,所以第一个L1 的值变了