Loops in Python: For and While Loops Explained

Quick answer: Learn Python for and while loops, including range, break, continue, else clauses on loops, and nested loops, with practical examples.

For Loops

A for loop iterates over a sequence, such as a list, string or range of numbers.

fruits = ['apple', 'banana', 'cherry']

for fruit in fruits:
    print(fruit)

Using range()

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

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

While Loops

A while loop repeats as long as a condition remains true.

count = 0

while count < 5:
    print(count)
    count += 1

Forgetting to update the loop variable is the most common cause of an infinite loop.

Break and Continue

for num in range(10):
    if num == 5:
        break        # exits the loop entirely
    print(num)

for num in range(10):
    if num % 2 == 0:
        continue     # skips to the next iteration
    print(num)       # prints only odd numbers

The else Clause on a Loop

A loop's else block runs only if the loop completes normally, without hitting a break.

for num in [2, 4, 6, 8]:
    if num % 2 != 0:
        print("Found an odd number")
        break
else:
    print("All numbers are even")   # this runs, since no break occurred

Nested Loops

for i in range(3):
    for j in range(2):
        print(i, j)

Looping with enumerate() and zip()

fruits = ['apple', 'banana', 'cherry']

for index, fruit in enumerate(fruits):
    print(index, fruit)

prices = [50, 30, 80]
for fruit, price in zip(fruits, prices):
    print(fruit, price)

For vs While: Which to Use

Use a for loop when you know in advance what you are iterating over, such as a list or a fixed range. Use a while loop when the number of iterations depends on a condition that can only be checked at runtime.

Common Interview Questions

What is the difference between break and continue?

break exits the loop entirely. continue skips only the current iteration and moves to the next one.

When does a loop's else clause execute?

Only when the loop finishes all its iterations without encountering a break statement.

How do you avoid an infinite while loop?

Ensure the condition being checked is actually updated inside the loop body, so it will eventually become false.