Diagonal Stripe Field

By the end of this lab you'll be able to:

• Use setheading() to point the turtle in any compass direction
• Translate a loop counter into a starting coordinate to space shapes evenly
• Use penup() and pendown() to reposition without drawing

Thirty parallel diagonal lines stripe the canvas from bottom-left to top-right, alternating teal and coral like a bold piece of fabric.

Welcome to the Diagonal Stripe Field!

In this lab you'll learn how to aim the turtle at any angle and draw long lines across the entire canvas. One formula turns a loop counter into a starting position. Let's code it together!

How the Stripes Work

Each stripe is a diagonal line drawn at a 45° angle. The turtle: 1. Lifts the pen and jumps to a starting position along the bottom edge 2. Aims at exactly 45° with setheading(45) 3. Draws a long line across the canvas

The starting x position is computed as -300 + i * 20 — so stripe 0 starts at x = -300, stripe 1 at x = -280, stripe 2 at x = -260, and so on, spacing them 20 pixels apart.

setheading() vs right()

right(n) turns relative to where Monty is already facing. setheading(n) sets an absolute compass heading: 0° = East, 90° = North, 45° = North-East. Use setheading() when you always want the exact same angle, regardless of prior turns.

Sample Code

import turtle
monty = turtle.Turtle()
monty.speed(0)
monty.hideturtle()
monty.pensize(3)

colors = ['teal', 'coral']

for i in range(30):
    monty.color(colors[i % 2])
    monty.penup()
    monty.goto(-300 + i * 20, -250)
    monty.pendown()
    monty.setheading(45)
    monty.forward(500)

What Do You Think Will Happen?

There are 30 stripes and 2 colors alternating. How many teal stripes will appear? Make your guess — then click Run to find out!

Try It Now

▶ Run ↻ Reset

30 ÷ 2 = 15 teal stripes (and 15 coral). Were you right?

How It Works

monty.goto(-300 + i * 20, -250) is the key line. When i = 0 the turtle starts at (-300, -250) — the lower-left corner. Each increment of i shifts the starting x position 20 pixels to the right, spreading the stripes evenly.

setheading(45) is called inside the loop to reset the angle each time, because the previous forward(500) leaves Monty pointing in the same direction, but it's good practice to set it explicitly.

Explanation Table

Line	What it does
monty.pensize(3)	Thicker lines so stripes are clearly visible
colors[i % 2]	Alternates teal (even i) and coral (odd i)
monty.goto(-300 + i * 20, -250)	Positions each stripe 20px to the right of the last
monty.setheading(45)	Points Monty exactly North-East for a 45° diagonal
monty.forward(500)	Draws a long diagonal line across the canvas

Learning Check

Your Turn — Add the Heading

The program below draws 30 lines but they all go horizontally — no diagonal! Add one line after monty.pendown() to make every stripe go at 45°.

▶ Run ↻ Reset

The missing line is monty.setheading(45) — heading 45° points exactly North-East.

Experiments

1. Change the angle. Replace setheading(45) with setheading(60). Stripes get steeper. Try setheading(30) for a shallower angle. You'll know it worked when the stripes visibly tilt.

2. Change stripe spacing. Replace i * 20 with i * 10. Stripes are denser. You'll know it worked when the lines nearly overlap.

3. Add more colors. Change colors to ['teal', 'coral', 'gold'] and i % 2 to i % 3. You'll know it worked when three colors cycle across the stripes.

4. Vary the line width. Replace monty.pensize(3) with monty.pensize(1 + i // 5). Early stripes are thin, later ones thick. You'll know it worked when the stripe widths visibly grow.

Wonderful Work!

You learned to combine goto(), setheading(), and a loop counter formula to tile an entire canvas with diagonal lines — a technique used in every graphics program! Up next: Dotted Grid to explore the dot() command and size mapping.