reverse() does not work on a Python literal?

Why doesn't this work in Python?

>>> print [0,1,0,1,1,0,1,1,1,0,1,1,1,1,0].reverse() 
None

I expected to ge开发者_如何学运维t back the list in reverse order.

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>>> a = [3, 4, 5]
>>> print a.reverse()
None
>>> a
[5, 4, 3]
>>>

It's because reverse() does not return the list, rather it reverses the list in place. So the return value of a.reverse() is None which is shown in the print.

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If you want it to return a new list in reverse order, you can use [::-1]

>>> [0,1,0,1,1,0,1,1,1,0,1,1,1,1,0][::-1]
[0, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 0, 1, 0]

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As I'm still trying to understand the downvote, if it doesn't matter that the original list gets changed, use @taskinoor's answer, it'll be faster.

However if you're required to keep the original list unchanged, I suggest you to use [::-1].

from time import time
lst = [0,1,0,1,1,0,1,1,1,0,1,1,1,1,0]

s = time()
for i in xrange(5000000):
    a = lst[::-1]          # creates a reversed list
print time() -s

s = time()
for i in xrange(5000000):
    b = lst[:]             # copies the list
    b.reverse()            # reverses it
print time() -s

outputs

2.44950699806
3.02573299408

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If you want reversed copy of a list, use reversed:

>>> list(reversed([1,2,3,4]))
[4, 3, 2, 1]

p.s. reversed returns an iterator instead of copy of a list (as [][::1] does). So it is suitable then you need to iterate through a reversed iterable. Additional list() here used only for the demonstration.

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Just to complement other answers. Do not forget:

>> reversed_iterator = reversed([0,1,0,1,1,0,1,1,1,0,1,1,1,1,0])
>> print list(reversed_iterator)
[0, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 0, 1, 0]

This way your list is unchanged if this is a requierement.

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reverse changes a list variable as seen here list reverse

if you print it after you reversed it it will show up correctily

so just use a variable