ይህ ትምህርት ገና ወደ አማርኛ አልተተረጎመም፤ ስለዚህ በእንግሊዝኛ ቀርቧል። የእንግሊዝኛውን ገጽ ክፈቱ

break, continue, and loop else

4 min read

Sometimes a loop should end early: you found what you were looking for. Sometimes one round should be skipped: a value is obviously wrong. In this lesson you'll do both with break and continue, meet a loop feature that even experienced programmers misread, and combine several loop plans into one program that handles messy input.

Stop at the first one: break

You met break in lesson 3.1: it leaves the loop at once. It's how you stop a search as soon as it succeeds. Which number from 50 to 99 is the first multiple of 7?

for n in range(50, 100):
    if n % 7 == 0:
        print("First multiple of 7:", n)
        break

Ctrl or Cmd + Enter runs

Without the break, it would print every multiple up to 98. Remove it and see. If loops are inside each other, break leaves only the loop it's in; lesson 3.4 shows that. And break belongs to loops only, not to if:

የተለመደ ስህተት

This breaks

price = -5
if price < 0:
    break

Python says

SyntaxError: 'break' outside loop

The fix

price = -5
if price < 0:
    print("Price can't be negative")

An if isn't a loop, so there's nothing to break out of. An if block simply ends where its indentation ends. Python checks this before running anything, which is why it's a SyntaxError.

Skip one round: continue

continuecontinueSkips the rest of the current round and goes straight to the next one. skips the rest of the current round, and the loop carries on with the next one. Predict what this counts.

ውጤቱን ገምቱ

Decide before you look. Guessing wrong is how this sticks.

count = 0
for n in range(1, 8):
    if n % 3 == 0:
        continue
    count = count + 1
print(count)

Python prints

The loop runs for 1 to 7. For 3 and 6, continue skips the rest of the round, so count isn't increased. The other five numbers are counted.

That's how you skip bad values. Someone typed four prices, and two are negative by mistake. Skip those and add up the rest:

total = 0
count = 0
for i in range(4):
    price = int(input("Price: "))
    if price < 0:
        continue
    total = total + price
    count = count + 1
print(f"{count} prices, {total} birr")

Ctrl or Cmd + Enter runs

Input

One answer per line, given to input() in order.

The loop's else

A loop can have an else, and most people guess wrong about when it runs. Predict.

ውጤቱን ገምቱ

Decide before you look. Guessing wrong is how this sticks.

for letter in "Abel":
    if letter == "e":
        print("Found e")
        break
else:
    print("No e")
for letter in "Hana":
    if letter == "e":
        print("Found e")
        break
else:
    print("No e")

Python prints

Found e
No e

In the first loop, break runs, so the else is skipped. The second loop finishes without a break (there's no e in Hana), so its else runs.

A loop's else runs only when the loop finished without a break. It's not "otherwise", and it doesn't mean "if the loop never ran". Many experienced programmers misread it, so read it as "no break". It's useful for exactly this job: a search, with a message when nothing was found.

ጥያቄ

When does a for loop's else block run?

Best so far

To find the highest score, keep the best so far: compare each new score with it, and replace it when the new one is higher. Start it below any possible score, so the first score always wins.

Keeping the highest

Press Next to run one line at a time and watch each name change.Each row is one step: the line that just ran, and every name's value after it.

When it asks, the user types 67, 82, then 45።

1highest = -1
2for i in range(3):
3    score = int(input("Score: "))
4    if score > highest:
5        highest = score
6print("Highest:", highest)

Names and their values after line 1
Name	Value after line 1
highestbest so far	-1new
icounter	not made yet
scorelatest value	not made yet

Output so far

Score: 67
Score: 82
Score: 45
Highest: 82

Step 1 of 14

Every step: the line that ran and each name's value after it
Step	Line	highestbest so far	icounter	scorelatest value	Printed
1	1	-1	not made yet	not made yet
2	2	-1	0	not made yet
3	3	-1	0	67	Score: 67
4	4	-1	0	67
5	5	67	0	67
6	2	67	1	67
7	3	67	1	82	Score: 82
8	4	67	1	82
9	5	82	1	82
10	2	82	2	82
11	3	82	2	45	Score: 45
12	4	82	2	45
13	2	82	2	45
14	6	82	2	45	Highest: 82

Three plans in six lines: i is a counter, score is the latest value, and highest is the best so far. At step 12, 45 isn't higher than 82, so line 5 is skipped and highest keeps 82.

መልመጃ

Exam averages

Read exam scores until the user types -1. Skip any score outside 0 to 100, with a message. Then print how many scores were valid and their average, to one decimal. If there were no valid scores, print No valid scores instead of crashing. Also try it with only -1 in the Input box.

This is a famous problem, known as the Rainfall problem. Researchers have given it to beginners for decades, and many studies report low success rates. The hard part isn't the syntax; it's combining the plans. Yours needs five: a stop value (-1 ends the loop with break), skipping bad input (continue), a running total, a counter, and a guard so you never divide by zero.

Output

Score (-1 to stop): 72
Score (-1 to stop): 105
Skipped: 105
Score (-1 to stop): 88
Score (-1 to stop): 64
Score (-1 to stop): -1
3 scores, average 74.7

Your code

total = 0
count = 0
# Ask until -1, skip scores outside 0-100, then print the count and average

Ctrl or Cmd + Enter runs

Input

One answer per line, given to input() in order.

መፍትሄውን አሳይ

This is one way to solve it, not the only one. If yours prints the same thing, it works.

total = 0
count = 0
while True:
    score = int(input("Score (-1 to stop): "))
    if score == -1:
        break
    if score < 0 or score > 100:
        print("Skipped:", score)
        continue
    total = total + score
    count = count + 1
if count > 0:
    print(f"{count} scores, average {total / count:.1f}")
else:
    print("No valid scores")

ዋና ዋና ነጥቦች

break leaves the loop at once; use it to stop a search when it succeeds.
continue skips the rest of this round and goes on to the next; use it to skip bad values.
A loop's else runs only when the loop ended without break. Read it as "no break".
Best so far: compare each value with the best, and replace the best when the new one wins.
Real programs combine plans: stop value, skip bad input, running total, counter, and a guard.