Effect of cache-unfriendly array access in python

pymem.py

import time
import random

size = 1000000 # more zeros, more difference

nums = list(range(size))
inds = list(range(size))

# reset cache
sum(nums)
sum(inds)

# sum in memory order
st = time.time()
total = 0
for i in inds:
    total += nums[i]
print(total, (time.time() - st)*1e6)

# randomize indexes
random.shuffle(inds)

# reset cache
sum(nums)
sum(inds)

# sum in random order
st = time.time()
total = 0
for i in inds:
    total += nums[i]
print(total, (time.time() - st)*1e6)