Triangle Spiral in Python Turtle

Beginner · Patterns and spirals · 25 lines · draws in about 14 seconds

A triangle turns 120 degrees at each corner, and turning 122 instead, with every line a little longer, twists the triangles into a three-armed spiral.

Triangle Spiral in Python Turtle: the finished drawing

import turtle

screen = turtle.Screen()

screen.bgcolor("black")

screen.title("Triangle spiral")

t = turtle.Turtle()

t.speed(10)

t.pensize(2)

colors = ["magenta", "cyan", "yellow"]

# Start a little higher, so the finished spiral sits in the middle

t.penup()

t.goto(0, 20)

t.pendown()

# A triangle turns 120 degrees at each corner; 122 makes it twist as it grows

for i in range(1, 155):

t.pencolor(colors[i % 3])

t.forward(i * 2.5)

t.left(122)

t.hideturtle()

turtle.done()

Open in the editor

How the code works

Three colours and a starting point

One colour for each side of a triangle, so each arm of the spiral keeps its own colour. The turtle starts 20 steps above the centre because the finished spiral reaches a little further down than up.

colors = ["magenta", "cyan", "yellow"]

# Start a little higher, so the finished spiral sits in the middle
t.penup()
t.goto(0, 20)
t.pendown()

The twisting loop

i counts from 1 to 154 and each line is i * 2.5 steps long, so every side is longer than the one before. The extra 2 degrees at each corner add up and turn the whole triangle a little further on every lap.

# A triangle turns 120 degrees at each corner; 122 makes it twist as it grows
for i in range(1, 155):
    t.pencolor(colors[i % 3])
    t.forward(i * 2.5)
    t.left(122)

Make it yours

Change the code above and press Run. Some ideas:

Change t.left(122) to t.left(120) to see the plain triangle spiral without the twist.
Change t.left(122) to t.left(125) for a stronger twist.
Add "lime" to the list and change i % 3 to i % 4 so the colours wind around the arms.

What it uses

Every turtle command the site supports is listed on Python turtle online.