Python for loops and while loops

Loops

Python has two loop types. Use for when the number of iterations is known; use while when looping until a condition changes.

For Loop

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

for i in range(2, 10, 2):  # 2 4 6 8
    print(i)

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

While Loop

count = 0
while count < 5:
    print(count)
    count += 1  # always modify the condition variable

Break and Continue

for n in range(10):
    if n == 3:
        continue   # skip 3
    if n == 7:
        break      # stop at 7
    print(n)       # 0 1 2 4 5 6

A for/while loop can have an else block that runs only when the loop finishes without hitting break. Guard every while loop with a clear exit condition or a counter — missing this causes infinite loops.

A common mistake with while loops is forgetting to update the loop variable, causing an infinite loop. If you accidentally start one in the terminal, press Ctrl+C to interrupt. The range() function does not create a list — it returns a lazy range object that generates values on demand, making it memory-efficient even for large counts. When iterating over a sequence and also needing the index, use enumerate(iterable) instead of manually tracking a counter. This is more idiomatic and less error-prone.