How to Break out of multiple loops in Python

In this tutorial, we will learn how to break out of multiple loops and to do this there are two methods for breaking out of multiple loops and they are using a Flag Variable and Exceptions.

Using a Flag Variable:

This method uses a Boolean flag variable to control the loop termination.

• Flag Initialization: At the beginning of the outer loop, initialize the flag variable to ” False “.
• Flag Usage: Within the nested loops, whenever want to break out of all loops, set the flag to ” True “.
• Condition Check: Before each loop iteration, check the flag variable . If it’s” Ture “, break out of the outer loop using ” break “.

Example: In the provided example below, flag is initially set to False. Inside the inner loop, if j equals 3, flag is set to True, causing the outer loop to break.

flag = False
for i in range(5):
    if flag:
        break
    for j in range(5):
        if j == 3:
            flag = True 
            break 
        print(i, j)

 

Output:

0 0
0 1
0 2
1 0
1 1 
1 2
2 0
2 1
2 2 
3 0
3 1
3 2
4 0 
4 1
4 2

This output demonstrates the iterations of the nested loops until the condition ‘ j == 3 ‘ is met in the inner loop. Once ‘ j ‘ reaches ‘ 3 ‘, the outer loop breaks due to the flag being set to ‘ True ‘, and the execution stops.

Using Exceptions:

This method uses custom exceptions to break out of nested loops.

• Exception Definition: Define a custom exception class, such as “ BreakLoop “.
• Loop Execution: Within the loops, whenever want to break out, raise the custom exception.
• Exception Handling: The outer loop is wrapped in a ” try-except ” block. When the custom exception is raised, the execution jumps to the ” except ” block.

Example: In the provided example below, when j equals 3, the BreakLoop exception is raised, causing the execution to jump out of the nested loops.

class BreakLoop(Exception):
    pass
try:
    for i in range(5):
        for j in range(5):
            if j == 3:
                raise
BreakLoop
            print(i, j)
except BreakLoop:
    pass

Output: Here the output is same for both the codes because both methods achieve the same result of breaking out the loops when ‘ j == 3 ‘ is met in the inner loop. Once the ‘ BreakLoop ‘ exception is raised, the execution jumps to the ‘ except ‘ block, effectively terminating the nested loops.

Both methods offer a way to break out of multiple loops in python, proving flexibility based on your coding preferences and specific requirements.