For Loop & Range

range() generates a sequence of numbers and is most often used to control a for loop. range(stop) counts from 0 up to — but not including — stop.

print(list(range(5)))

You can also give it a start and a step: range(start, stop, step).

print(list(range(2, 11, 2)))
print(list(range(10, 0, -1)))

A for loop runs its block once for every item in a sequence — a range, a string, a list, or anything else iterable.

for i in range(3):
    print("Count:", i)

for letter in "Hi!":
    print(letter)

Loops can be nested inside each other — handy for anything grid-shaped, like printing a pattern:

for i in range(4):
    for j in range(i + 1):
        print("*", end=" ")
    print()

While Loop

A while loop keeps running its block as long as a condition stays True. Unlike a for loop, it doesn't know in advance how many times it'll run, which makes it useful when you're waiting for something to change.

counter = 0
while counter < 3:
    print("Current count:", counter)
    counter += 1

Forgetting to update the variable in the condition creates an infinite loop, since the condition never becomes False:

# Careful - this never stops on its own:
while True:
    print("Looping forever...")

Break & Continue

break exits the loop immediately, skipping any remaining iterations entirely.

for i in range(10):
    if i == 5:
        print("Stopping at 5.")
        break
    print(i)

continue skips just the rest of the current iteration and moves on to the next one — the loop keeps going.

for i in range(5):
    if i == 2:
        continue
    print(i)