Loops

What it means

Python has two loop constructs: for (iterates over items in a sequence — a list, string, range, etc.) and while (repeats as long as a condition stays true). break exits a loop early; continue skips to the next iteration; loops also support an else clause that runs only if the loop completes without hitting a break.

Examples

for fruit in ["apple", "banana", "cherry"]:
    print(fruit)

for i in range(5):          # 0, 1, 2, 3, 4
    print(i)

count = 0
while count < 3:
    print(count)
    count += 1

for n in range(10):
    if n == 5:
        break                # stop the loop entirely
    if n % 2 == 0:
        continue             # skip to the next iteration
    print(n)                 # prints 1, 3

for i, value in enumerate(["a", "b", "c"]):
    print(i, value)          # 0 a / 1 b / 2 c

Common mistake

Writing while True: without a reliable way to exit — an easy way to accidentally write an infinite loop, especially if the condition that should trigger break never becomes true due to a logic bug.

# Risk of infinite loop if user never enters "quit"
while True:
    command = input("Enter command: ")
    if command == "quit":
        break
    process(command)

# Safer pattern with an explicit, bounded condition
attempts = 0
while attempts < 5:
    if try_connect():
        break
    attempts += 1

Quick practice

What’s the difference between break and continue?

Answer
break exits the loop entirely; continue skips the rest of the current iteration and moves to the next one.
What does enumerate() give you that a plain for item in list: doesn’t?

Answer
Both the index and the value on each iteration, without manually tracking a counter.
When does a loop’s else clause execute?

Answer
Only if the loop finishes normally, without hitting a break.