6. Turtle rectangle progressions

The code progressions below draw a rectangle.

With each version, an improvement in code structure is made.

Firstly, only sequencing is used, with no iteration.

Secondly, iteration, using a for-loop, reduces code duplication.

Thirdly, a definition block with parameters allows for code reuse via the use of arguments.

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6.1. Sequencing: steps to draw a rectangle

The code below uses sequencing only.

The code below draws a rectangle of side length 120 and width 50 at coordinates (20, 30).

The start direction, eastwards, is set by: t.seth(0)

The start position, at (20, 30), is set by: t.goto(20, 30).

t.pu() and t.pd() are used either side of it to avoid line drawing when repositioning the turtle.

A line is drawn forwards by: t.fd(120).

The turtle then turns to the left by: t.lt(90).

A line is drawn forwards by: t.fd(50).

The turtle then turns to the left by: t.lt(90).

Then the last 2 sides are drawn by doing the same 4 steps again.

Code Completion: rectangle steps

Q

Complete the code to draw a rectangle of side length 120 and width 50 at (20, 30), by replacing the XXXs.

import turtle

s = turtle.Screen()
s.bgcolor("white")
s.title("rectangle")
s.setup(width=800, height=600, startx=0, starty=0)

t = turtle.Turtle()
t.speed(5)

t.pu()
XXX(20, 30)
t.pd()
t.seth(0)

XXX(120)
XXX(90)
XXX(50)
XXX(90)
XXX(120)
XXX(90)
XXX(50)
XXX(90)

s.exitonclick()

Ans

Completed code to draw a rectangle of side length 120 and width 50 at (20, 30).

import turtle

s = turtle.Screen()
s.bgcolor("white")
s.title("rectangle")
s.setup(width=800, height=600, startx=0, starty=0)

t = turtle.Turtle()
t.speed(5)

t.pu()
t.goto(20, 30)
t.pd()
t.seth(0)

t.fd(120)
t.lt(90)
t.fd(50)
t.lt(90)
t.fd(120)
t.lt(90)
t.fd(50)
t.lt(90)

s.exitonclick()

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Tasks

1. From the code above, list the 8 lines that do the actual drawing.

2. From the 8 lines, list the simplest amount of code that is repeated to form a rectangle.

Q1

From the code above, list the lines that do the actual drawing.

t.fd(120)
t.lt(90)
t.fd(50)
t.lt(90)
t.fd(120)
t.lt(90)
t.fd(50)
t.lt(90)

Q2

From the 8 lines, list the simplest amount of code that is repeated to form a rectangle.

t.fd(120)
t.lt(90)
t.fd(50)
t.lt(90)

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6.2. Iteration: using a for-loop to draw a rectangle

The code below uses iteration to reduce code duplication that was present when only sequencing was used.

The code below draws a rectangle of side length 120 and width 50 at coordinates (20, 30).

Firstly, 2 sides are drawn, then this is repeated.

The iterator used is “_”. This is the standard choice in python when the iterator is not referenced in the for-loop block.

Code Completion: rectangle for loops

Q

Complete the code to draw a rectangle of side length 120 and width 50 at (20, 30), by replacing the XXXs.

import turtle

s = turtle.Screen()
s.bgcolor("white")
s.title("rectangle")
s.setup(width=800, height=600, startx=0, starty=0)

t = turtle.Turtle()
t.speed(5)

t.pu()
XXX(20, 30)
t.pd()
t.seth(0)

for _ in range(XXX):
    XXX(120)
    XXX(90)
    XXX(50)
    XXX(90)

s.exitonclick()

Ans

Completed code to draw a rectangle of side length 120 and width 50 at (20, 30).

import turtle

s = turtle.Screen()
s.bgcolor("white")
s.title("rectangle")
s.setup(width=800, height=600, startx=0, starty=0)

t = turtle.Turtle()
t.speed(5)

t.pu()
t.goto(20, 30)
t.pd()
t.seth(0)

for _ in range(2):
    t.fd(120)
    t.lt(90)
    t.fd(50)
    t.lt(90)

s.exitonclick()

---

Tasks

1. Modify the code above to draw a rectangle of 80 by 150.

Q1

Modify the code above to draw a rectangle of 80 by 150.

import turtle

s = turtle.Screen()
s.bgcolor("white")
s.title("rectangle")
s.setup(width=800, height=600, startx=0, starty=0)

t = turtle.Turtle()
t.speed(5)

t.pu()
t.goto(20, 30)
t.pd()
t.seth(0)

for _ in range(2):
    t.fd(80)
    t.lt(90)
    t.fd(150)
    t.lt(90)

s.exitonclick()

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6.3. Definitions: using a def block to draw a rectangle

The code below uses a definition block to draw a rectangle.

The function has parameters to specify the side length and the starting position of the bottom left vertex.

The function also requires the turtle to be passed as an argument so it can be referred to.

Before the for-loop, the turtle is repositioned without drawing the movement; penup and pendown are needed for that.

rectangle(t, length=40, width=30, start_pos=(0, 0), start_h=0)

t - the turtle object to draw the rectangle

length - side length; default 40

width - side width; default 30

start_pos - start position; default (0, 0)

start_h - start heading; default 0 degrees

In the code below, rectangle(t) draws a default rectangle.

rectangle(t, length=120, width=50, start_pos=(20, 30)) draws a rectangle of 120 by 50 at (20, 30).

rectangle(t, length=400, width=300, start_pos=(-300, -100), start_h=10) draws a rectangle of 400 by 300 at (-300, -100) with an angle of 10 degrees.

Code Completion: rectangle definition

Q

Complete the code to draw a rectangle of side length 120 and width 50 at (20, 30), by replacing the XXXs.

import turtle

s = turtle.Screen()
s.bgcolor("white")
s.title("rectangle")
s.setup(width=800, height=600, startx=0, starty=0)

t = turtle.Turtle()
t.speed(5)


def rectangle(t, XXX=40, XXX=30, XXX=(0, 0), XXX=0):
    t.pu()
    t.goto(XXX)
    t.pd()
    t.seth(XXX)

    for _ in range(2):
        t.fd(XXX)
        t.lt(90)
        t.fd(XXX)
        t.lt(90)


rectangle(t)
rectangle(t, length=120, width=50, start_pos=(20, 30))
rectangle(t, length=400, width=300, start_pos=(-300, -100), start_h=10)

s.exitonclick()

Ans

Completed code to draw a rectangle of side length 120 and width 50 at (20, 30).

import turtle

s = turtle.Screen()
s.bgcolor("white")
s.title("rectangle")
s.setup(width=800, height=600, startx=0, starty=0)

t = turtle.Turtle()
t.speed(5)


def rectangle(t, length=40, width=30, start_pos=(0, 0), start_h=0):
    t.pu()
    t.goto(start_pos)
    t.pd()
    t.seth(start_h)

    for _ in range(2):
        t.fd(length)
        t.lt(90)
        t.fd(width)
        t.lt(90)


rectangle(t)
rectangle(t, length=120, width=50, start_pos=(20, 30))
rectangle(t, length=400, width=300, start_pos=(-300, -100), start_h=10)

s.exitonclick()

---

Tasks

1. Modify the code above to draw a rectangle of 80 by 150 at (-80, -150).

Q1

Modify the code above to draw a rectangle of 80 by 150 at (-80, -150).

import turtle

s = turtle.Screen()
s.bgcolor("white")
s.title("rectangle")
s.setup(width=800, height=600, startx=0, starty=0)

t = turtle.Turtle()
t.speed(5)

def rectangle(t, length=40, width=30, start_pos=(0, 0), start_h=0):
    t.pu()
    t.goto(start_pos)
    t.pd()
    t.seth(start_h)

    for _ in range(2):
        t.fd(length)
        t.lt(90)
        t.fd(width)
        t.lt(90)


rectangle(t, length=80, width=150, start_pos=(-80, -150), start_h=0)

s.exitonclick()

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6.4. Adding pen colour and fill colour parameters

The syntax below adds parameters for pen and fill colours.

rectangle(t, length=40, width=30, start_pos=(0, 0), start_h=0, penw=1, penc='black', fillc=None)

t - the turtle object to draw the rectangle

length - side length; default 40

width - side width; default 30

start_pos - start position; default (0, 0)

start_h - start heading; default 0 degrees

penw - pensize; default 1

penc - pencolor; ; default “black”

fillc - fillcolor; default None

In the code below, rectangle(t, length=400, width=300, start_pos=(-100, -150), start_h=10, penw=5, penc="black", fillc="light green") draws a rectangle of 400 by 300 at (x=-100, y=-150) with a black pencolor, a green fillcolor, using a pensize of 5.

The code needs to check the fillc argument since setting a fillcolor to None will throw an error.

Code Completion: rectangle_steps_coloured definition

Q

Complete the code to draw a rectangle of side length 120 and width 50 at (20, 30), by replacing the XXXs.

import turtle

s = turtle.Screen()
s.bgcolor("white")
s.title("rectangle")
s.setup(width=800, height=600, startx=0, starty=0)

t = turtle.Turtle()
t.speed(0)


def rectangle(t, length=40, width=30, start_pos=(0, 0), start_h=0,
                XXX=1, XXX="black", XXX=None):
    t.pu()
    t.goto(start_pos)
    t.pd()
    t.seth(start_h)

    t.pensize(XXX)
    t.pencolor(XXX)

    if XXX is not None:
        t.fillcolor(XXX)
        t.begin_fill()

    for _ in range(2):
        t.fd(length)
        t.lt(90)
        t.fd(width)
        t.lt(90)

    if XXX is not None:
        t.end_fill()


rectangle(t, length=400, width=300, start_pos=(-100, -150), start_h=10,
            penw=5, penc="black", fillc="light green")

s.exitonclick()

Ans

Completed code to draw a rectangle of side length 120 and width 50 at (20, 30).

import turtle

s = turtle.Screen()
s.bgcolor("white")
s.title("rectangle")
s.setup(width=800, height=600, startx=0, starty=0)

t = turtle.Turtle()
t.speed(0)


def rectangle(t, length=40, width=30, start_pos=(0, 0), start_h=0,
                penw=1, penc="black", fillc=None):
    t.pu()
    t.goto(start_pos)
    t.pd()
    t.seth(start_h)

    t.pensize(penw)
    t.pencolor(penc)

    if fillc is not None:
        t.fillcolor(fillc)
        t.begin_fill()

    for _ in range(2):
        t.fd(length)
        t.lt(90)
        t.fd(width)
        t.lt(90)

    if fillc is not None:
        t.end_fill()


rectangle(t, length=400, width=300, start_pos=(-100, -150), start_h=10,
            penw=5, penc="black", fillc="light green")

s.exitonclick()

---

Tasks

1. Use the definition provided above to draw a rectangle of side lengths 150 and 250 at (x=-150, y=-250) with a purple pencolor, a bisque fillcolor, with a pensize of 10.

Q1

Use the definition provided above to draw a rectangle of side lengths 150 and 250 at (x=-150, y=-250) with a purple pencolor, a bisque fillcolor, with a pensize of 10.

import turtle

s = turtle.Screen()
s.bgcolor("white")
s.title("rectangle")
s.setup(width=800, height=600, startx=0, starty=0)

t = turtle.Turtle()
t.speed(0)

def rectangle(t, length=40, width=30, start_pos=(0, 0), start_h=0,
                penw=1, penc="black", fillc=None):
    t.pu()
    t.goto(start_pos)
    t.pd()
    t.seth(start_h)

    t.pensize(penw)
    t.pencolor(penc)

    if fillc is not None:
        t.fillcolor(fillc)
        t.begin_fill()

    for _ in range(2):
        t.fd(length)
        t.lt(90)
        t.fd(width)
        t.lt(90)

    if fillc is not None:
        t.end_fill()


rectangle(t, length=150, width=250, start_pos=(-150, -250), start_h=0,
            penw=10, penc="purple", fillc="bisque")

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6.5. Practice Questions

Exercises

1. Using sequencing only, draw a rectangle of side lengths 500 and 400 at (-250, -250).

2. Using a repeat loop (without a function), draw a rectangle of side lengths 50 and 40 at (-25, -25).

3. Use the definition provided above to draw a rectangle of side lengths 400 and 300 at (x=-300, y=-200) with a black pencolor, a snow fillcolor, with a pensize of 6.