The range() Function

Concept: for loops

range() produces a sequence of numbers to loop over — handy when you want to repeat something a set number of times, or step through a run of values.

range(stop)

Counts from 0 up to but not including stop:

for i in range(5):
    print(i)

This prints 0, 1, 2, 3 and 4, each on its own line: five iterations in total. The stop value 5 is not included.

range(start, stop)

Counts from start up to but not including stop:

for face in range(2, 7):
    print(face)

range(2, 7) gives 2, 3, 4, 5, 6. The stop value 7 is never reached — a neat way to step through the faces of a die that aren't 1.

The stop value is left out

This trips up nearly everyone at first: the number you pass as stop is not included. To include a number, aim one past it. list() shows the whole sequence at once:

print(list(range(1, 10)))
print(list(range(1, 11)))

The first one stops at 9. To get all the way to 10, the stop value has to be 11.

Optional: choosing a step

A third argument specifies how much the value changes each time:

for number in range(2, 9, 2):
    print(number)

This prints 2, 4, 6 and 8, on separate lines. The stop value is still excluded.

A negative step counts down:

for number in range(3, 0, -1):
    print(number)

This prints 3, 2 and 1. You do not need the step argument for Repeated Greetings or Times Table.

For positions in a non-empty string of length n, the last index is n - 1. A negative step must move towards a smaller, excluded stop. With range(2, -1, -1), the values are 2, 1 and 0; -1 itself is not visited. If the starting value already equals the stop, the range is empty.

Counting while you loop

range() pairs naturally with a running count — see the accumulator pattern.

Your turn

Add a loop that uses range() to print the numbers 1 to 5 — remember, the stop value is left out.

# add a two-line loop using range()

Expected output

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