Python Tutorial — Learn Python Step by Step

Python while Loop

The while loop repeats as long as a condition is True. Use it when you don't know in advance how many iterations are needed.

Basic while Loop

# Count from 1 to 5
count = 1
while count <= 5:
    print(count, end=" ")
    count += 1
# Output: 1 2 3 4 5

# Sum until threshold
total = 0
num = 1
while total < 100:
    total += num
    num += 1
print(f"Sum reached {total} after adding {num-1} numbers")

while with else

# else block runs when condition becomes False (NOT on break)
n = 5
while n > 0:
    print(n, end=" ")
    n -= 1
else:
    print("Loop completed normally!")
# Output: 5 4 3 2 1 Loop completed normally!

Practical Examples

# Input validation loop
while True:
    age = input("Enter age (1-120): ")
    if age.isdigit() and 1 <= int(age) <= 120:
        age = int(age)
        break
    print("Invalid! Try again.")

# Retry with max attempts
attempts = 0
max_attempts = 3
while attempts < max_attempts:
    password = input("Password: ")
    if password == "secret":
        print("Access granted!")
        break
    attempts += 1
    print(f"Wrong. {max_attempts - attempts} attempts left.")
else:
    print("Account locked.")

• while True + break is a common pattern for input validation.
• The else clause runs only if the loop exits without break.
• Always ensure the condition variable changes — otherwise infinite loop.