Techniques for Exiting Nested Loops in Python

Python provides two primary loop structures— while loops and for loops. When a non‑prime number is entered in a game scenario, the program must terminate both the inner prime‑checking loop and the outer input loop.

Using the Same Condition to Break Each Loop

This straightforward approach places a break in both the inner and outer loops, each triggered by the same condition (finding a divisor).

<code># This program demonstrates breaking out with the same condition; input 2 will raise an error
while True:
    number = int(input('Please input an integer: '))
    for i in range(2, number):
        if number % i == 0:
            break
    if number % i == 0:
        break
print('Game Over')
</code>

Using a Flag Variable

A boolean flag is set to True before the inner loop. If a divisor is found, the flag becomes False and the inner break stops that loop; the outer loop then checks the flag and breaks as well.

<code>while True:
    number = int(input('Please input an integer: '))
    flag = True  # assume number is prime
    for i in range(2, number):
        if number % i == 0:
            flag = False
            break
    if not flag:
        break
print('Game Over')
</code>

Raising an Exception

If break cannot achieve the desired effect, a custom exception (e.g., StopIteration ) can be raised inside the inner loop and caught outside to exit all loops.

<code>try:
    while True:
        number = int(input('Please input an integer: '))
        for i in range(2, number):
            if number % i == 0:
                raise StopIteration
except StopIteration:
    print('Game Over')
</code>

Combining else with Loops

Python’s else clause on loops runs only when the loop finishes without a break . By placing a break in the outer loop’s else , we can ensure a single exit point after the inner loop succeeds.

<code>while True:
    number = int(input('Please input an integer: '))
    for i in range(2, number):
        if number % i == 0:
            break
    else:
        continue
    break
print('Game Over')
</code>

Using a Function Return

Encapsulating the nested loops inside a function allows a return statement to terminate the entire process as soon as a non‑prime is detected.

<code>def prime_game():
    while True:
        number = int(input('Please input an integer: '))
        for i in range(2, number):
            if number % i == 0:
                return
prime_game()
print('Game Over')
</code>

All the above techniques provide flexible ways to exit nested loops in Python, each suited to different coding styles and requirements.