Transcript EOP CS Component

Class 2
Introduction to turtle graphics
Today’s Topics
First steps
 Turtle graphics
 Python modules
 Python help and documentation
 for and range
 def – creating a function
Computing is a social activity
If you’ve got a question, ask it (it’s part
of computing culture)
 We’re working in pairs. It’s more fun,
more real and more productive.
 Use the online help system and tutorial
 Use the textbook
 Ask a TA or tutor
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Introduction to Turtle Graphics
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Type ‘from turtle import *’ and press enter
 This gives you access to the functions in Python’s turtle
module
 A module is a collection of functions
 ‘*’ matches everything
Type:
 pendown() and press enter
 forward(100) and press enter
 A new window pops up and a straight line will be
drawn
Why are the pendown() parens empty? What is the
‘100’ in the parens?
Introduction to Turtle Graphics
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Some useful commands
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forward(distance)
left(degrees)
right(degrees)
goto(xcoord, ycoord)
up() – (no drawing)
down() – (pen ‘down’ for drawing)
clear()
Look up the Turtle module in the Python docs
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Python manuals > Global module index > Turtle (Tk)
Practice Drawing Shapes
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Draw the following shapes using forward(),
left() or right()
 Triangle, square or rectangle, pentagon,
dodecagon
Challenge problem 1: Draw a set of squares
rotated at different angles
Challenge problem 2: Draw a set of squares offset
from each other (hint: use ‘up’)
Write down the sequence of Python statements
you used before you exit (you’ll need them later)
Write your own function
Use def to create your own function
 Put this function definition is a file
def square(size):
forward(size)
right(90)
forward(size)
right(90)
forward(size)
right(90)
forward(size)
right(90)
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The for loop
Try this
>>> for i in 'cat':
print(i)
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Now try this
>>> for i in range(3):
print('cat')
 Use for in range() to improve your square
function
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