speedtest_reverse_xrange.md

Short Conclusion

xrange is faster than range, reverse almost as fast as -1

I found reversed used in combination with xrange in one of the Python standard library, it should be fine.

https://hg.python.org/cpython/file/2.7/Lib/heapq.py

import timeit
MAX = 500000
cnt = 0
t = timeit.default_timer()
for i in reversed(range(MAX)):
  cnt+=i
print 'reversed  range: ', timeit.default_timer() - t,cnt

cnt = 0
t = timeit.default_timer()
for i in reversed(xrange(MAX)):
  cnt+=i
print 'reversed xrange: ', timeit.default_timer() - t, cnt

cnt = 0
t = timeit.default_timer()
for i in range(MAX-1,-1,-1):
  cnt+=i
print ' step -1  range: ', timeit.default_timer() - t, cnt

cnt=0
t = timeit.default_timer()
for i in xrange(MAX-1,-1,-1):
  cnt+=i
print ' step -1 xrange: ', timeit.default_timer() - t, cnt