3.8. Loop Control

In this section, we'll learn about two statements that are used to control a loop's flow.

break statement

The break statement is used to interrupt the loop and terminate it. This statement will terminate the loop immediately regardless of whether the loop condition is True or not.

Using a while loop

CodeOutput

while True:  # (1)!
    password = input('Enter password: ')

    if password == 'python':
        break

    print('Invalid Password')

print('Access granted')

1. while True: indicates a loop that runs forever or until break statement is not executed.

Enter password: wrong
Invalid Password
Enter password: random input
Invalid Password
Enter password: python
Access granted

(Highlighted lines are inputs)

In above while loop example, the program will repeatedly prompt for password until the correct one is not entered, in this case python.

Using a for loop

CodeOutput (gun)Output (london)Output (practice)

word = input('Enter a word')

for char in word:
    if char == 'a':
        print('letter A found in word')
        break

    print(char)

Enter a word: gun
g
u
n

(Highlighted lines are inputs)

Enter a word: london
l
o
n
d
o
n

(Highlighted lines are inputs)

Enter a word: practice
p
r
letter A found in word

(Highlighted lines are inputs)

In this example, the program takes a word as input and prints its characters. As soon as an a character is found, the program outputs a message and loop terminates.

continue statement

The continue statement is used to continue to next iteration without executing the rest of loop body.

Using a while loop

CodeOutput

x = 1

while x <= 10:
    if x == 3:
        continue

    result = x * 2
    print('2', '*', x, '=', result)
    x = x + 1

2 * 1 = 2
2 * 2 = 4
2 * 4 = 8
2 * 5 = 10
2 * 6 = 12
2 * 7 = 14
2 * 8 = 16
2 * 9 = 18
2 * 10 = 20

Above program prints the times table for 2 however it doesn't print the multiple of 2 with 3.

Using a for loop

The same program could be written with a for loop.

CodeOutput

for x in range(1, 11)
    if x == 3:
        continue

    result = x * 2
    print('2', '*', x, '=', result)

2 * 1 = 2
2 * 2 = 4
2 * 4 = 8
2 * 5 = 10
2 * 6 = 12
2 * 7 = 14
2 * 8 = 16
2 * 9 = 18
2 * 10 = 20