Understanding Python while Loops: Syntax, Variants, and Control Statements

Python provides two loop constructs, for and while; the while loop repeats a block of statements as long as a given condition evaluates to True.

Basic while syntax :

while <condition>:
    # statement block

The loop continues while the condition is true; once it becomes false, execution proceeds after the loop.

Example – sum of numbers 1 to 100 :

sum = i = 0
while i <= 100:  # loop condition
    sum = sum + i
    i += 1   # equivalent to i = i + 1
print(sum)  # outputs 5050

while … else … (rarely used) executes the else block after the loop finishes normally:

while <condition>:
    # while block
else:
    # else block

Example – sum of odd numbers up to 100:

sum = i = 0
while (2 * i + 1) <= 100:  # loop condition
    sum = sum + 2 * i + 1
    i += 1
else:
    print('Loop ended')
print(sum)

Infinite loops occur when the condition is always true. Example shows reading integers until a negative number is entered:

key = 1
while key >= 0:
    key = input('Please enter a positive integer:')
    key = int(key)
    if key >= 100:
        print(key, 'not less than 100')
    else:
        print(key, 'less than 100')

Be careful: an always‑true condition creates a dead loop unless an explicit break is used.

break terminates the loop immediately, while continue skips the rest of the current iteration and proceeds to the next one.

Break example (stops when i == 3):

i = 0
while i <= 5:  # loop condition
    if i == 3:
        break  # exit loop
    print(i)
    i += 1

Output: 0, 1, 2

Continue example (skips printing when i == 3):

i = 0
while i <= 5:  # loop condition
    i += 1
    if i == 3:
        continue  # skip this iteration
    print(i)

Output: 1, 2, 4, 5, 6

Summary : The while loop is a condition‑controlled loop that runs while its expression is true; it ends when the expression becomes false. break ends the loop entirely, whereas continue skips the current iteration and proceeds to the next.