Loop

Code that repeats, either over items (for) or while a condition holds (while).

A loop runs the same block of code more than once. A for loop repeats once per item in a sequence (a list, string, range, and so on), binding each item to a variable in turn. A while loop keeps going as long as a condition stays True. Inside either, break stops the loop early and continue skips to the next round.

Example 
for n in [1, 2, 3]:       # once per item
    print(n)

count = 0
while count < 2:          # repeat while the condition holds
    count += 1
print("done", count)
Output 
1
2
3
done 2

Where this shows up in real Python

Loops do the repetitive work: processing each file, row, or item; retrying until something succeeds; or building a list one piece at a time.

Commonly used Loop tools

  • range(n) — loop a fixed number of times
  • enumerate(seq) — loop with an index
  • zip(a, b) — loop over two sequences together
  • break / continue — stop early / skip to the next item
  • [x for x in seq] — a comprehension — a loop that builds a list

Official documentation: Python Tutorial: for Statements

Related lessons

Related terms