Class 2 Introduction to turtle graphics

1. Class 2Introduction to turtle graphics

2. Today’s Topics First steps • Turtle graphics • Python modules • Python help and documentation • for and range • def – creating a function

3. 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

4. Introduction to Turtle Graphics • 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?

5. Introduction to Turtle Graphics • Some useful commands • 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 • Python manuals > Global module index > Turtle (Tk)

6. Practice Drawing Shapes • 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)

7. 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)

8. The for loop • Try this >>> for i in 'cat': print(i) • Now try this >>> for i in range(3): print('cat') • Use for in range() to improve your square function