The continue Statement

1How it is written

for value in values:
    statement
    if this one should be skipped:
        continue          <- jumps back up to the header
    statement             <- not run on a skipped round

next statement

Like break, it is a keyword and a single-word statement written inside a loop body, and like break it lives under an if — a bare continue would skip the rest of the body on every round, which makes the lines below it pointless.

2Printing 1 to 10, minus the multiples of 4

# print 1 to 10, but skip anything divisible by 4
for i in range(1, 11):
    if i % 4 == 0:
        continue
    print(i)

1
2
3
5
6
7
9
10

4 and 8 are missing, and everything else is there. On those two rounds i % 4 == 0 was True, continue ran, and print(i) was skipped — but the loop went on to the next value as if nothing had happened.

3Step through it

The tracer again, this time on continue. The round where i is 4 is the one to watch: the pointer jumps from the jump line back up to the header, and 4 never reaches the output.

nothing yet

4What it is really for: skipping the odd one out

Real data has gaps in it. A marks list might use -1 to mean the paper was never submitted — and that value must not be added to the total or counted as a paper:

# -1 means the paper was not submitted
marks = [78, -1, 92, -1, 65]
total = 0
count = 0

for m in marks:
    if m == -1:
        continue
    total = total + m
    count = count + 1

print('Papers marked:', count)
print('Total marks:', total)

Papers marked: 3
Total marks: 235

Two lines were skipped twice, and the other three rounds ran in full. A break here would have been a disaster: the loop would have stopped at the first -1 and the last three marks would never have been seen.

5Every continue can be written as an if

Here is something worth knowing before an exam asks: continue never adds anything Python could not already do. Turn the condition round, put the work inside it, and the continue disappears:

# the same program written without continue
for i in range(1, 11):
    if i % 4 != 0:
        print(i)

1
2
3
5
6
7
9
10

Identical output, one line shorter. continue said “if it is a multiple of 4, skip it”; this says “if it is not a multiple of 4, print it”. Same rule, stated the other way round.

6The trap: continue in a while loop

In a for loop, continue is safe — the header hands out the next value by itself. A while loop has no header doing that. You update the variable, in the body — and continue skips the rest of the body.

Put the update before the skip and all is well:

# the update comes first, so continue cannot skip it
i = 0

while i < 5:
    i = i + 1
    if i == 3:
        continue
    print(i)

1
2
4
5

Put it after, and the program hangs. When i is 3, the continue jumps back to the condition without ever reaching i = i + 1, so i is 3 again, and again, for ever. It prints 0, 1 and 2 and then stands still — not ending, just never getting anywhere:

# DO NOT RUN THIS — it never stops
i = 0

while i < 5:
    if i == 3:
        continue
    print(i)
    i = i + 1

7Nothing after it runs either

Just like break, anything written after a continue in the same block is unreachable — the jump has already happened:

for i in range(1, 4):
    continue
    print('this line never runs')

print('done')

done

8Try it

Change continue to break in the program below and run it again. One adds four readings and reaches 59; the other gives up at the first negative number and reaches 12.

# add up only the readings that make sense
readings = [12, -5, 18, 20, -3, 9]
total = 0

for r in readings:
    if r < 0:
        continue
    print('Adding', r)
    total = total + r

print('Total:', total)

9Recap