[Solved] Reverse the list while creation

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Well designed test shows that first function is slowest on Python 2.x (mostly because two lists have to be created, first one as a increasing range, second one as a reverted first one). I also included a demo using reversed.

from __future__ import print_function
import sys
import timeit

def iterate_through_list_1(arr):
    lala = None
    for i in range(len(arr))[::-1]:
        lala = i

def iterate_through_list_2(arr):
    lala = None
    for i in range(len(arr), 0, -1):
        lala = i

def correct_iterate_reversed(arr):
    lala = None
    for obj in reversed(arr):
        lala = obj


print(sys.version)
print('iterate_through_list_1', timeit.timeit('iterate_through_list_1(seq)',
                                              setup='from __main__ import iterate_through_list_1\nseq = range(0, 10000)',
                                              number=10000))
print('iterate_through_list_2', timeit.timeit('iterate_through_list_2(seq)',
                                              setup='from __main__ import iterate_through_list_2\nseq = range(0, 10000)',
                                              number=10000))
print('correct_iterate_reversed', timeit.timeit('correct_iterate_reversed(seq)',
                                                setup='from __main__ import correct_iterate_reversed\nseq = range(0, 10000)',
                                                number=10000))

Results:

2.7.12 (default, Jun 29 2016, 14:05:02) 
[GCC 4.2.1 Compatible Apple LLVM 7.3.0 (clang-703.0.31)]
iterate_through_list_1 3.87919592857
iterate_through_list_2 3.38339591026
correct_iterate_reversed 2.78083491325

Differences in 3.x are all neglible, because in each case objects iterated over are lazy.

3.5.2 (default, Jul 28 2016, 21:28:00) 
[GCC 4.2.1 Compatible Apple LLVM 7.3.0 (clang-703.0.31)]
iterate_through_list_1 2.986786328998278
iterate_through_list_2 2.9836046030031866
correct_iterate_reversed 2.9411962590020266

solved Reverse the list while creation