Question

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 get back the list in reverse order.

Answer 1

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