range(): make a list of numbers to count through
range() makes a run of numbers for you to count through — 0, 1, 2, 3... — without typing them out. Loops use it to know how many times to go.
The big idea
range(n) makes the numbers 0 up to (but not including) n.
See it in code
First, let's just look at the numbers range makes. Wrap it in list(...) to see them all at once:
print("range(5) gives:", list(range(5)))
print("range(3) gives:", list(range(3)))range(5) gives: [0, 1, 2, 3, 4] range(3) gives: [0, 1, 2]
See how range(5) stopped at 4, not 5? It makes five numbers, but it starts at 0.
Those numbers are counters you can use. A loop walks through range(5), and we turn each number i into an x-spot — sliding a little further across each time:
for i in range(5):
print("star", i, "at x", 90 + i * 80)star 0 at x 90 star 1 at x 170 star 2 at x 250 star 3 at x 330 star 4 at x 410
90 + i * 80 turns 0, 1, 2, 3, 4 into 90, 170, 250 … — five evenly spaced spots from one line of math. Next we hand those spots to real stars.
Now put it on the canvas. The loop counts through range(5), and we place a star at each x-spot — the same 90 + i * 80 from above:
from art import Canvas, star
screen = Canvas.create()
Canvas.fill(screen)
print("range(5) gives:", list(range(5)))
for i in range(5):
star(screen, 90 + i * 80, 250, size=50)range(5) gives: [0, 1, 2, 3, 4]
Five numbers from range(5), five stars on the canvas. Change the 5 to 8 and you get eight stars — no extra typing.
range is the counter behind most loops. Repeat a sound three times, draw ten rows, take twenty steps — range hands the loop the exact numbers to count through. Change the count, change how many times things happen.
Try it yourself
Change range(5) to range(8) — the printout and the stars both grow. Then try range(1, 4), which starts at 1 and gives 1, 2, 3.
The common mistake
Expecting range(5) to include 5. It stops before the number you give, so range(5) is 0, 1, 2, 3, 4. To count up to and include 5, write range(6) or range(1, 6).
What it unlocks
range powers for loops, and once you nest two loops with it you can fill a grid with nested loops.