Flag Tutorial: Romania to Colombia

Beginning Python programmers can use this tutorial to learn basic concepts in Python using the visual tools in the turtle module. All the code runs in your browser, so you don’t have to install anything.

The challenge in this tutorial is to learn how this turtle script draws the Romanian flag on the right, 300 pixels wide and 200 high with colours in vertical bars. Then change it to draw the Colombian flag shown in the goal canvas below, with the same colours in a different order and in horizontal bars. You can experiment on your own, or read the rest of the tutorial to learn the concepts you need. The progress bar shows how close you are to the goal, and the canvas differences, below right, highlight the differences in red.

If you really mess up the script, you can click the reset button to go back to the start. If you want more challenge, try the next tutorial with the flags of Japan and Burkina Faso.

Table of Contents

• The Challenge
• Moving the Turtle
• Debugging with Stamps
• Filling Shapes
• Repeating with Loops
• Lifting the Pen
• Changing Colour

The Challenge

### Canvas ###
import turtle as t

t.penup()
t.left(90)
t.forward(100)
t.right(90)
t.back(150)
t.write('Romania', font=('Arial', 30))

t.color('dodgerblue4')
t.begin_fill()
for i in range(2):
    t.forward(100)
    t.right(90)
    t.forward(200)
    t.right(90)
t.end_fill()
t.forward(100)

t.color('gold')
t.begin_fill()
for i in range(2):
    t.forward(100)
    t.right(90)
    t.forward(200)
    t.right(90)
t.end_fill()
t.forward(100)

t.color('firebrick3')
t.begin_fill()
for i in range(2):
    t.forward(100)
    t.right(90)
    t.forward(200)
    t.right(90)
t.end_fill()

t.done()
### Goal ###
import turtle as t

t.penup()
t.back(150)
t.left(90)
t.forward(100)
t.write('Colombia', font=('Arial', 30))
t.back(100)

t.color('gold')
t.begin_fill()
for i in range(2):
    t.forward(100)
    t.right(90)
    t.forward(300)
    t.right(90)
t.end_fill()
t.back(50)

t.color('dodgerblue4')
t.begin_fill()
for i in range(2):
    t.forward(50)
    t.right(90)
    t.forward(300)
    t.right(90)
t.end_fill()
t.back(50)

t.color('firebrick3')
t.begin_fill()
for i in range(2):
    t.forward(50)
    t.right(90)
    t.forward(300)
    t.right(90)
t.end_fill()

Moving the Turtle

If you haven’t used the turtle before, imagine that it’s a little turtle in the middle of a piece of paper with a pen in its mouth. You can tell it to walk forward and backward or turn left and right. When it walks, it drags the pen along the paper and draws a line. It always starts in the middle of the page, facing right.

In this example, it walks forward 100 pixels with forward(), turns 90° to the right using right(), then walks forward 50 pixels . Use left() if you want to turn left and backward() if you want to go backward. The done() call at the end doesn’t do anything here in the browser, but it keeps the turtle window open, if you copy this script and run it in regular Python. Can you change the script so that your canvas matches the goal canvas below?

### Canvas ###
import turtle as t

t.forward(100)
t.right(90)
t.forward(50)

t.done()
### Goal ###
import turtle as t

t.forward(50)
t.right(45)
t.forward(100)

Debugging with Stamps

Two moves plus a turn are pretty simple to follow, but the scripts will get longer and more complicated. When you’re trying to figure out how a script works, the stamp() method can show you where the turtle is at any point. In this script, the stamp shows you where the turtle starts. Try cutting that line and then pasting it after each command in the script. Think about where you expect the stamp to appear before you paste it in. You can also move the current line up and down with Alt+Up and Alt+Down on most systems or Option+Up and Option+Down on a Mac. You can find more shortcuts in the Ace editor documentation.

Bonus: If you want to change the shape of the cursor to a turtle, add t.shape("turtle") on the second line in this script.

### Canvas ###
import turtle as t

t.stamp()
t.forward(100)
t.right(30)
t.forward(84)
t.right(60)
t.forward(66)
t.right(90)
t.forward(50)
t.right(120)
t.forward(33)
t.right(150)
t.forward(16)

t.done()

Filling Shapes

To draw the flags, you need to fill in blocks of colour, calling begin_fill(), moving the turtle around a shape, and then calling end_fill(). Turn this triangle into a square.

### Canvas ###
import turtle as t

t.begin_fill()
t.forward(100)
t.right(120)
t.forward(100)
t.end_fill()

t.done()
### Goal ###
import turtle as t

t.begin_fill()
for _ in range(4):
    t.forward(100)
    t.right(90)
t.end_fill()

If you get stuck with the left side of the square highlighted in red, make sure you’ve moved the turtle around all four sides of the square. It makes a small difference.

Repeating with Loops

Computers are good at doing the same thing over and over. Drawing a square, for example, can be done by repeating two commands four times: move forward and turn 90°. One way to repeat commands in Python is to put them in a for loop. The range() function produces a range of numbers, and for i in range(4): will repeat the commands below it 4 times, putting a different number in i each time. In this example, we don’t care about the number in i, we just want to repeat the movements 4 times. Which lines are inside the loop? Python uses indentation (a tab or four spaces) to group lines into a loop, so the loop ends when the indentation comes back to the left.

Try changing this square into a rectangle. As a hint, rectangles are less repetitive than squares, so your loop will only repeat two times, but it will have two different forward moves in it.

### Canvas ###
import turtle as t

for i in range(4):
    t.forward(50)
    t.left(90)

t.done()
### Goal ###
import turtle as t

for i in range(2):
    t.forward(100)
    t.left(90)
    t.forward(50)
    t.left(90)

Lifting the Pen

The turtle doesn’t have to draw a line everywhere it moves. Try moving the penup() and pendown() calls around in this script to see what changes. Try adding a t.stamp() call.

### Canvas ###
import turtle as t

t.begin_fill()
for i in range(2):
    t.forward(100)
    t.left(90)
    t.forward(50)
    t.left(90)
t.end_fill()

t.right(90)
t.forward(50)
t.left(90)
t.penup()
t.forward(50)
t.pendown()
for i in range(4):
    t.forward(50)
    t.right(90)

t.done()

Changing Colour

The last thing you need to solve this challenge is changing the colour of the pen with the color() command. Can you figure out how to add the gold rectangle below the blue square?

### Canvas ###
import turtle as t

t.color('blue')
t.begin_fill()
for i in range(4):
    t.forward(50)
    t.left(90)
t.end_fill()

t.done()
### Goal ###
import turtle as t

t.color('blue')
t.begin_fill()
for i in range(4):
    t.forward(50)
    t.left(90)
t.end_fill()

t.penup()
t.right(90)
t.forward(50)
t.left(90)
t.back(50)
t.pendown()
t.color('gold')
t.begin_fill()
for i in range(2):
    t.forward(100)
    t.right(90)
    t.forward(50)
    t.right(90)
t.end_fill()

Now that you have all the skills you need, can you solve the challenge at the start of the tutorial? Here’s a summary of the skills you learned: