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Is it cheaper to flip the attached list or add a list? - python

Which is faster and more pythonic?

  • cancel added list
  • start adding a list from the very beginning
  • through deque

eg. here ome ready data to store in a new list

# Let say my function outputs these output individually.
x = [12,34,44,346,345,876,123]

Change of attached list:

new_list = []
for i in x:
  new_list.append(i)
new_list = newlist[::-1]

Providing a list:

new_list = [] 
for i in x:
  new_list.insert(0,i)

Using deque:

from collections import deque
for i in x:
  x.appendleft(i)

Please note that my question is not a reverse listing. Also assume that this list is ~ 20,000 in size.

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Your first method can be simplified to one line:

new_list = x[::-1]

Then, to check which method is faster than any other, just use timeit

(tested with python 2.7.8):



C:\>python -m timeit -s "x = [12,34,44,346,345,876,123]" "new_list = x[::-1]"
1000000 loops, best of 3: 0.215 usec per loop

C:\>python -m timeit -s "x = [12,34,44,346,345,876,123]; new_list = []" "for i in x:" "  new_list.insert(0,i)"
10000 loops, best of 3: 146 usec per loop

C:\>python -m timeit -s "from collections import deque; x = [12,34,44,346,345,876,123]; new_list = deque()" "for i in x:" "  new_list.appendleft(i)"
1000000 loops, best of 3: 0.713 usec per loop

C:\>python -m timeit -s "x = [12,34,44,346,345,876,123]" "new_list = list(reversed(x))"
1000000 loops, best of 3: 0.837 usec per loop

So, new_list = x[::-1]

better than any other.

You should also ask yourself if you want to "link" or "copy" items into the new list structure.

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