146 – Cycling over an iterable

Whenever you need to cycle over an iterable use itertools.cycle:

from itertools import cycle

servers = [...]

for server in cycle(servers):
    server.ping()

This is preferred over the modulo operator trick:

servers = [...]
idx = 0

while True:
    idx = (idx + 1) % len(servers)
    servers[idx].ping()

The two main advantages are that

1. cycle is more readable because the name spells out what you are doing; and

2. the modulo operator trick has limitations, since it only works on iterables that you can index and compute the length of.