5.4 Break and continue

Learning objectives

By the end of this section you should be able to

Analyze a loop's execution with break and continue statements.
Use break and continue control statements in while and for loops.

Break

A break statement is used within a for or a while loop to allow the program execution to exit the loop once a given condition is triggered. A break statement can be used to improve runtime efficiency when further loop execution is not required.

Ex: A loop that looks for the character "a" in a given string called user_string. The loop below is a regular for loop for going through all the characters of user_string. If the character is found, the break statement takes execution out of the for loop. Since the task has been accomplished, the rest of the for loop execution is bypassed.

user_string = "This is a string."
for i in range(len(user_string)):
  if user_string[i] == 'a':
    print("Found at index:", i)
    break

Note

Infinite loop

A break statement is an essential part of a loop that does not have a termination condition. A loop without a termination condition is known as an infinite loop. Ex: An infinite loop that counts up starting from 1 and prints the counter's value while the counter's value is less than 10. A break condition is triggered when the counter's value is equal to 10, and hence the program execution exits.

counter = 1
while True:
  if counter >= 10:
    break
  print(counter)
  counter += 1

Continue

A continue statement allows for skipping the execution of the remainder of the loop without exiting the loop entirely. A continue statement can be used in a for or a while loop. After the continue statement's execution, the loop expression will be evaluated again and the loop will continue from the loop's expression. A continue statement facilitates the loop's control and readability.

Try It

Using break control statement in a loop

Write a program that reads a string value and prints "Found" if the string contains a space character. Else, prints "Not found".

usr = input()

# Printing the given input
print("You have entered", usr)

# TODO: identify if the string contains a space character

Try It

Using a continue statement in a loop

Complete the following code so that the program calculates the sum of all the numbers in list my_list that are greater than or equal to 5.

my_list = [1, 5, 7, 12, 5, 17, 9, 2, 4]

total = 0

for i in my_list:
    if i < 5:
        # TO DO: numbers less than 5 should be skipped.

   else: 
        # TO DO: numbers greater than 5 should be summed up.

print(total)

Adapted from Introduction to Python Programming by OpenStax (openstax.org), licensed under CC BY-NC-SA 4.0. Changes were made. License: CC-BY-NC-SA-4.0.