Break, Continue, Pass, Loop Else, and Nesting

break

break exits the nearest enclosing loop immediately; statements after the loop may still run, but the current loop body stops.

for n in range(5):
    if n == 3:
        break
    print(n)

This prints 0, 1, 2. When n becomes 3, break exits before the print.

In nested loops, break exits only the inner loop that contains it; the outer loop continues.

for row in range(2):
    for col in range(3):
        if col == 1:
            break
        print(row, col)

The outer loop advances to the next row after each inner break. Python has no labeled break, so to leave both loops you need a flag or a function return.

continue

continue skips the rest of the current iteration. In a for loop Python moves to the next iterable value; in a while loop it returns to the condition check.

for n in range(5):
    if n % 2 == 0:
        continue
    print(n)

This prints 1 and 3. Even numbers hit continue, so their print is skipped. The dangerous version is a while loop whose counter update sits below continue — that update is skipped and the loop can run forever.

pass

pass does nothing. It is a placeholder where Python's grammar requires a statement but you have no action yet.

for n in range(3):
    if n == 1:
        pass
    print(n)

This prints 0, 1, 2. pass does not mean skip the rest of the block; it performs no action and execution continues to the next statement. Contrast the three:

Loop else

Python allows else on both for and while. The loop else runs only if the loop finished without executing break.

for ch in 'abc':
    if ch == 'x':
        print('found')
        break
else:
    print('missing')

This prints missing because the loop never breaks. Had a break fired, the else would be skipped. Read loop else as "no break happened," not as the negation of the loop condition. This is a textbook search pattern: break on a hit, else to report no hit.

Nested-loop trace table

Finish the entire inner loop for one outer value before moving on. Use columns for each piece.

This prevents the most common error: believing a single break exits all loops. It also makes continue easy to follow because you can mark exactly which iteration was skipped.

Exam traps

Check indentation before deciding whether an else belongs to an if or to a loop. Remember that break suppresses only the else attached to the loop it leaves. Remember that continue does not end the loop; it advances to the next iteration. Treat pass as a syntactically valid blank line, not a hidden control command. And recall that break/continue outside any loop raise a SyntaxError.

continue in a while loop is the dangerous case

In a for loop, continue is safe because the loop variable advances automatically from the iterable. In a while loop, continue returns to the condition test and can skip the very statement that updates the counter.

i = 0
while i < 5:
    if i == 2:
        continue   # i is never incremented again
    print(i)
    i += 1

When i reaches 2, continue jumps back to the test with i still 2, looping forever. The fix is to update i before continue. Recognizing this infinite-loop pattern is a frequent PCEP exam item.

break exits one level only

Because Python has no labeled break, leaving nested loops requires a flag or wrapping the loops in a function and using return.

found = False
for row in grid:
    for cell in row:
        if cell == target:
            found = True
            break
    if found:
        break

The inner break leaves the inner loop; the outer if found: break then leaves the outer loop. The exam wants you to know a single break cannot escape both at once.

Loop else as a search reporter

The for/else idiom is the canonical "search and report" pattern. The else says no break happened, meaning nothing was found.

nums = [2, 4, 6]
for n in nums:
    if n % 2 == 1:
        print('odd found')
        break
else:
    print('all even')

No odd value exists, so the loop completes without breaking and the else prints all even.

Quick-reference behavior table

Final tracing routine

For nested or control-heavy snippets: complete the inner loop fully for each outer value; mark each break/continue/pass event in its own row; verify which loop a break actually exits; and only after the trace decide whether any loop else runs. This disciplined approach is what lets you finish the Control Flow questions — the largest slice of the exam — accurately within the time limit.