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)
t.pensize(3)
colours = ["purple", "mediumpurple", "royalblue", "hotpink"]
count = 0
for size in range(20, 220, 20):
t.pencolor(colours[count % 4])
for side in range(4):
t.forward(size)
t.left(90)
count = count + 1
t.hideturtle()
turtle.done()Think about it
- How many squares will there be?
- Where do all the squares start?
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.