Python · control flow

Loop Else

A loop's else block runs only when the loop finishes without break.

Two ways out of a loop

Read else on a loop as "no break".

For-else basics


        # else runs if no break
        for i in range(5):
            if i == 10:
                break
        else:
            print("Loop completed")
        # ans: Loop completed

While-else basics


        # else runs after while completes
        count = 0
        while count < 3:
            print(count)
            count += 1
        else:
            print("Done")
        # ans: 0, 1, 2, Done

Break prevents else


        # break prevents else from running
        for i in range(5):
            if i == 3:
                break
        else:
            print("This won't print")
        # ans: nothing: break skips the else

Empty loop with else


        # else runs even if the loop is empty
        for i in range(0):
            pass
        else:
            print("Runs")
        # ans: Runs

Exercises

Does the else run? Predict, then press → to trace.

Exercise 1


        # does else run?
        for i in range(5):
            pass
        else:
            print("Done")
        # ans: Done (no break)

Exercise 2


        # what about this?
        for i in range(5):
            if i == 2:
                break
        else:
            print("Done")
        # ans: nothing (break prevents else)

Exercise 3


        # while-else?
        x = 0
        while x < 0:
            x += 1
        else:
            print("Else runs")
        # ans: Else runs (the body never executes, but there is no break)

Exercise 4


        # tricky: does else run?
        for i in range(0):
            pass
        else:
            print("Yes")
        # ans: Yes (empty range, no break)

Exercise 5


        # what prints?
        for i in range(3):
            if i == 5:
                break
        else:
            print("Complete")
        # ans: Complete (the condition is never True, so no break)

Exercise 6


        # while-else with break?
        x = 0
        while x < 3:
            if x == 2:
                break
            x += 1
        else:
            print("Done")
        # ans: nothing (break prevents else)

Exercise 7


        # nested loop else?
        for i in range(2):
            for j in range(2):
                if j == 1:
                    break
        else:
            print("Outer else")
        # ans: Outer else (the inner break doesn't affect the outer loop)

Exercise 8


        # what happens?
        for i in range(3):
            if i == 3:
                break
        else:
            print("Runs")
        # ans: Runs (range(3) stops at 2, so i == 3 is never True)

Exercise 9


        # while-else execution?
        x = 5
        while x < 3:
            x += 1
        else:
            print("Else")
        # ans: Else (the condition is False from the start)

Exercise 10


        # tricky break?
        for i in range(3):
            if False:
                break
        else:
            print("Complete")
        # ans: Complete (the break never executes)

Remember

else = "no break"

The else block runs when the loop ends normally.

break skips it

Leaving with break jumps past the else.

Empty loops count

A loop that never runs its body still ends normally, so else runs.

Only its own loop

A break in an inner loop doesn't stop the outer loop's else.