Challenge type: Turtle Challenges · Difficulty: ★★★★★ Super tricky · Language: Python
Real programmers read code and imagine what it will do. That’s called tracing. Have a go!
import turtle
t = turtle.Turtle()
t.speed(0)
turtle.bgcolor("black")
colours = ["mediumpurple", "orange", "seagreen", "purple"]
for i in range(72):
t.pencolor(colours[i % 4])
t.forward(i * 2)
t.left(90)
t.hideturtle()
turtle.done()Think about it
- Will the lines get longer or shorter?
- What shape does the spiral look like?
- How many colours will you see?
Need a hint?
Read the loop first. How many times does it repeat, and what does the turtle do each time? Draw it on paper one step at a time, turning your pencil like the turtle turns.
Grown-ups: This code runs in IDLE, the editor that comes with Python. Open a new file, paste the code, save it (any name except turtle.py) and press F5. A window opens and the turtle draws.
For teachers and grown-ups
Skills practised: Reading code, tracing loops, and connecting angles and shapes.
The big idea: Reading code and predicting what it does (tracing) is as important as writing it.
Questions to ask:
- How many times does the loop repeat?
- How far does the turtle turn altogether?
- Which single number would you change to make a different shape?
Take it further: Children sketch their prediction first, run the code in IDLE, then change one value and predict again.