Decomposition is when you break down problems into smaller sub-problems (chunks) so that they are easier to solve. If we were to breakdown this card into smaller chunks, it would be a lot easier to complete. 

Question:
How many chunks do you think we can split this card into?

Answer:
We should be left with the following:

1. The tree’s shape or leaves (3 triangles)
2. The tree’s trunk (1 rectangle)
3. The baubles on the tree (10 circles)
4. The text
5. The snowy ground (1 rectangle)
6. The Sky (Background)
7. The Snow (a lot of small circles)

We now have 7 different elements, however we can also take each element and further break it down. For example, the 3 triangles take make up the three leaves, you may ask, “How do we draw a triangle?”.

1. Create the triangle outlines, 2. Fill in the triangle.

import turtle
import random

snow_size = 4
snow_speed = 3
draw_speed = 10
rate_of_snow_balls = 6
width = 600
height = 600
screen = turtle.Screen()

Let’s start making the card already! First, let’s create the tree leaves, the 3 triangles. Unfortunately, Python’s Turtle does not know how to make triangles on its own, so we have to teach it how to. Also, because we will be using multiple triangles, we will use a Function.

A function is a piece of code we can use again and again.

Question:
Can you spot what other shape would we need to use again and again in this card?

Answer:
Circles! Yes, we use circles for the baubles as well as the snow!

Now lets make a function for triangles.

The Code:

def make_triangle(x, y, size, outline, triangle):
        triangle.hideturtle()
        triangle.penup()
        triangle.setposition(x, y)
        triangle.pensize(3)
        if outline:
        triangle.pendown()
        if not outline:
        triangle.fillcolor("forest green")
        triangle.begin_fill()
        triangle.setposition(x + size, y - size)
        triangle.setposition(x - size, y - size)
        triangle.setposition(x, y)
        if not outline:
            triangle.end_fill()

If you are attempting the extra challenges, lets create a function for circles as well (Optional):

def make_ball(x, y, size, colour, ball):
        ball.hideturtle()
        ball.penup()
        ball.setposition(x, y)
        ball.color(colour)
        ball.dot(size)

Now we have a variables and functions set, we have to tell our code, where the pieces should go. Since we have 3 triangles, we should use a loop, so we do not need to repeat or code 3 times.

•  A quick recap on Loops.

A loop is a program that repeats a sequence of instructions until a specific condition is met.

Question:
What kind of loop do you think we should use for the 3 triangles?

Answer:
Yes, it’s For Loops, because we know that we only need 3 triangles to create the tree.

The Code:

triangle_1 = turtle.Turtle()
triangle_1.speed(draw_speed)
outline = True
for repeat in range(2):
    make_triangle(0, width / 3, width / 6, outline, triangle_1)
    make_triangle(0, width / 4, width / 4, outline, triangle_1)
    make_triangle(0, width / 8, width / 3, outline, triangle_1)
    outline = False
screen.tracer(0)

To make the scene more alive we need to fill it with extra elements. We can start by drawing two simple rectangles, one smaller brown rectangle just under the tree leaves would be our tree trunk, and another larger white rectangle will make it appear as if the tree is on a snowy ground.

The Code: Snowy ground and Tree Trunk

stem = turtle.Turtle()
# white snowy ground
stem.penup()
stem.hideturtle()
stem.setposition(-width, -width / 3)
stem.color("white")
stem.begin_fill()
stem.setposition(width, -width / 3)
stem.setposition(width, -width / 2)
stem.setposition(-width, -width / 2)
stem.end_fill()
screen.update()
# tree trunk
stem.color("brown")
stem.setposition(-width / 30, -width / 4.8)
screen.tracer(1)
stem.pendown()
stem.begin_fill()
stem.setposition(width / 30, -width / 4.8)
stem.setposition(width / 30, -3 * width / 8)
stem.setposition(-width / 30, -3 * width / 8)
stem.setposition(-width / 30, -width / 4.8)
stem.end_fill()

The Code: Sky
We could also add a background colour for our sky:

screen.bgcolor("sky blue")

The Code: Message
Finally, our message “Happy Holidays” could be added, and of corse you can replace this with any message you would like!

text_1 = turtle.Turtle()
text_1.hideturtle()
text_1.penup()
text_1.setposition(0, 222)
text_1.color("white")
text_1.write("Happy Holidays",
             font=("Apple Chancery", 15, "bold"),
             align="center")

At this moment, you could complete the project by putting down

turtle.done()

and have a very classic holiday greeting card

However, you would like to further animate your card or take on a new challenge, you can try out Steps 7 and 8!