1. Survey of Computer Science CSCI 110, Spring 2011 Session 5 Conditionals Turtles

2. General Form for a Conditional
if condition: # condition is true or false
Python code A # Executed if condition is true
else:
Python code B # Executed if condition is false
Only one of the two blocks of code is executed.

3. General Form for using elif in a Conditional
if condition1: # condition is true or false
Python code A # Executed if condition1 is true
elif condition2:
Python code B #Executed if condition1 is false and 2 is true
else:
Python code C # Executed if conditions 1 and 2 are false
Only one of the blocks of code is executed.

4. Example Decision Tree "Enter your height: " height >= 75? true
false
print "Tall"
height >= 70?
true
false
print "Above average"
print "Short"

5. Program Example # Program height.py
height = input("Enter your height in inches: ")
if height >= 75:
print "Wow! You are tall!"
print "Please join our basketball team."
elif height >= 70:
print "You are above average height."
else:
print "You are shorter than average."
print "Thank you for participating in our survey."

6. Multiple decisions "Do you like to ski?" skiAns equals "yes"? true
false
"Downhill or cross country?"
"You should learn!"
response equals "downhill"?
true
false
"Try Wachusett"
"Try the local trails"
In Python, we use a nested conditional to program this decision tree.

7. Nested Conditional Example
# Program: downhill.py
skiAns = raw_input("Do you like to ski? ")
if skiAns == "yes":
response = raw_input("Downhill or cross country? ")
if response == "downhill":
print "Try Wachusett!"
else:
print "Try the local trails."
print "You should learn!"

8. Recall Classes and Objects
Python is an object oriented programming language.
All items of data are objects.
Objects have properties: Things that describe the objects
Objects have methods: Things an object can do.
A class describes a group of objects that have the same methods and set of properties.
Example: A car class
Properties: color, number of doors, body type
Methods: accelerate, brake, steer
My car is an object that is a member of the car class.

9. The Turtle Class
A turtle in python is an object from the Turtle class.
A turtle can move around a graphics window.
A turtle has a pen that can be up or down. If the pen is down, the turtle draws as it moves.
Turtle properties:
x (horizontal) position
y (vertical) position
direction (that it's facing)
pen position (up or down)
pen color

10. Turtle Methods Turtle methods:
forward(distance) Move forward <distance> pixels
backward(distance) Move backward <distance> pixels
right(angle) Turn right <angle> degrees
left(angle) Turn left <angle> degrees
up( ) Lift pen up
down( ) Put Pen down
goto(x, y) Move to position x, y
circle(radius) Draw a circle with a given radius.

11. Turtle Example #Use a turtle to draw a triangle.
from turtle import Pen as Turtle #import from library
yertle = Turtle( ) #Create a new Turtle object; name it yertle
yertle.forward(100) #Move yertle forward by 100 pixels
yertle.left(120) #Turn yertle left by 120 degrees