Loops

for, while, range and how to stop early.

for and range

A for loop walks anything you can iterate: a list, a string, a dict, a file. range(start, stop, step) counts up to but never including stop, so range(2, 8, 2) yields 2, 4 and 6.

enumerate(items) gives index and value together.
zip(a, b) walks two sequences side by side.

while and control

A while loop repeats until its condition fails, which suits waiting on something rather than walking a sequence. break leaves the loop immediately and continue skips to the next round.