Python Loop else Exercises

4 exercises that build on the Python else on Loops lesson, from easy to hard. Each one is checked in your browser when you press Check. Stuck? Use the hint before peeking at the solution.

What this lesson covers: The else block of a for or while loop runs once when the loop finishes normally, and is skipped when a break ends the loop. By the end you can write the search pattern with for ... else, check for primes, use else on a while loop, tell a loop's else from an if's else, and know when a flag is clearer. You will practise: Is the username free?; Predict the else; Fix the receipt search; Collect the primes up to 30.

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1. Is the username free?

Write code Easy

Loop over taken. If a name equals wanted, print <name> is taken and break. If the loop finishes without a break, print <name> is available using an else block on the loop. With the starting data the output is a single line: dina is available.

Your code

taken = ["asha", "ben", "chen"]
wanted = "dina"

# for ... else here

One possible solution

taken = ["asha", "ben", "chen"]
wanted = "dina"

for name in taken:
    if name == wanted:
        print(wanted, "is taken")
        break
else:
    print(wanted, "is available")

2. Predict the else

Predict the output Medium

Read the code and type exactly what it will print. Then press Check to run it and compare.

Read this code

count = 0
while count < 5:
    count += 1
    if count == 2:
        continue
    if count == 7:
        break
    print("count", count)
else:
    print("else ran")
print("end", count)

Your prediction — type the exact output

Actual output

count 1
count 3
count 4
count 5
else ran
end 5

3. Fix the receipt search

Fix the bug Medium

The code searches inbox for a subject that starts with Receipt. There is none, so it should print No receipt in the inbox once. It prints the message three times. Fix it.

Your code

inbox = ["Lunch?", "Invoice #204", "Newsletter"]
for subject in inbox:
    if subject.startswith("Receipt"):
        print("Found a receipt:", subject)
        break
    else:
        print("No receipt in the inbox")

One possible solution

inbox = ["Lunch?", "Invoice #204", "Newsletter"]
for subject in inbox:
    if subject.startswith("Receipt"):
        print("Found a receipt:", subject)
        break
else:
    print("No receipt in the inbox")

4. Collect the primes up to 30

Write code Hard

Build the list of prime numbers from 2 up to and including limit in primes, then print it. For every candidate, try each divisor from 2 up to the candidate minus 1 in an inner loop: break as soon as one divides evenly, and use the inner loop's else to append the candidate when none did.

Your code

limit = 30
primes = []

# for each number from 2 to limit, try the divisors in an inner loop
# break on a match; use else to add the prime to the list

One possible solution

limit = 30
primes = []

for number in range(2, limit + 1):
    for divisor in range(2, number):
        if number % divisor == 0:
            break
    else:
        primes.append(number)
print(primes)

Next lessonPython Nested Loops

More Python else on Loops examples · All Python exercises

Python Loop else practice exercises

1. Is the username free?

2. Predict the else

3. Fix the receipt search

4. Collect the primes up to 30