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For Loops: draw a whole row of stars from one line

A for loop is your shortcut for doing the same thing again and again. Watch one draw a whole row of stars from just three lines — it's one of the biggest ideas in all of coding.

The big idea

A for loop repeats the same steps over and over, counting as it goes — so you write the steps once instead of copying them.

See it in code

1Start simple

The simplest loop just repeats. range(3) means do this 3 times, and the indented line underneath is what gets repeated:

python
for i in range(3):
    print("Star!")
Run it — the same line, three times over:
Star!
Star!
Star!

Three trips around the loop, three lines. Change the 3 and you change how many times it runs.

2A step further

A loop also counts for you. Each time around, the loop variable i becomes the next number — and it starts at 0:

python
for i in range(5):
    print("Star number", i)
Run it — watch i count up as the loop goes:
Star number 0
Star number 1
Star number 2
Star number 3
Star number 4

See how i went 0, 1, 2, 3, 4? That counting is the secret — you can use i to make each trip a little different.

3In our world

Now the payoff: use that counter as a position. range(8) gives us 0 through 7, and we turn each i into an x-spot — sliding each star a little further to the right:

python
from art import Canvas, star

screen = Canvas.create()
Canvas.fill(screen)

for i in range(8):
    star(screen, 60 + i * 55, 250)
Run it, and eight stars line up across the canvas:
A row of eight bright yellow stars evenly spaced across a dark navy canvas.

One for line drew all eight stars. Want forty? Change the 8 to 40 — same three lines, no extra typing.

How a for loop draws a row of stars A flow chart. Start leads to "Draw a star", then "Move over a bit", then a decision "Any spots left?". If yes, the arrow loops back to draw another star. If no, it reaches Done. yes — keep going no Start Draw a star Move over a bit Any left? Done!
Each time around the loop: draw one star, move over, then ask “any spots left?” — until there are none.
The same idea, everywhere

A loop doesn't only draw stars. The same three lines can place a row of game characters, go through a list of names one at a time, or repeat any steps you'd otherwise copy-paste. Stars are just the easiest way to see a loop working.

Try it yourself

Change range(8) to range(20) and run it — twenty stars appear from the same three lines. Then swap the y (the 250) for i * 25 + 120 and make your stars climb like a staircase. Try it next time you're in a loop activity.

The common mistake

The classic oops: forgetting to use i. If you write star(screen, 60, 250) inside the loop (no i anywhere), every star lands in the exact same spot — so it looks like there's only one. The i is what makes each star show up somewhere new.

What it unlocks

Once one loop feels easy, loops inside loops fill the whole sky with rows and columns of stars, and the range() function lets you start, stop, and skip-count however you like.

Older, or want more depth? Read the Teens version →

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