Turtles

import turtle               # allows us to use the turtles library/module
window = turtle.Screen()        # creates a graphics window
alex = turtle.Turtle()      # create a turtle named alex
alex.forward(150)           # tell the object alex to move forward by 150 units invoking .forward method
alex.left(90)               # turn by 90 degrees
alex.forward(75)            # complete the second side of a rectangle

assign to alex “The Turtle type that is defined within the turtle module”

alex = turtle.Turtle()

• turtle starts off facing east when it is created (it is just part of the turtle library)

• Objects can have methods (things that they can do), and properties (things they are):

  • move_forward - m

  • jump - m

  • color - p

  • age - p

import turtle
window = turtle.Screen()
window.bgcolor("lightgreen")    # property

tess = turtle.Turtle()
tess.color("blue")              # property
tess.pensize(3)                    # property

tess.forward(50)                # method
tess.left(120)                    # method
tess.forward(50)                # method

window.exitonclick()            # method

Instances

Each instance has own properties, and methods.

import turtle
wn = turtle.Screen()             # Set up the window and its attributes
wn.bgcolor("lightgreen")


tess = turtle.Turtle()           # create tess and set some attributes
tess.color("hotpink")
tess.pensize(5)

alex = turtle.Turtle()           # create alex

tess.forward(80)                 # Let tess draw an equilateral triangle
tess.left(120)
tess.forward(80)
tess.left(120)
tess.forward(80)
tess.left(120)                   # complete the triangle

tess.right(180)                  # turn tess around
tess.forward(80)                 # move her away from the origin

alex.forward(50)                 # make alex draw a square
alex.left(90)
alex.forward(50)
alex.left(90)
alex.forward(50)
alex.left(90)
alex.forward(50)
alex.left(90)

wn.exitonclick()

For Loop

A basic building block of all programs is to be able to repeat some code over and over again. In computer science, we refer to this repetitive idea as iteration.

In Python, the for statement allows us to write programs that implement iteration.

for name in ["Joe", "Amy", "Brad", "Angelina", "Zuki", "Thandi", "Paris"]:
    print("Hi", name, "Please come to my party on Saturday!")

• name in this for statement is called the loop variable, it is being updated after each run

• list of names

• line 2 is the loop body !!! ALWAYS INDENTED

• terminating condition - if the conditions to iterate again are over, it is called t.c

• control flow aka. flow of execution of the program/loop is the name for python to know where in the loop we are at any given moment

  • sequential control flow == linear

control_flow

Iteration simplifies programs

import turtle            # set up alex
wn = turtle.Screen()
alex = turtle.Turtle()

for i in [0, 1, 2, 3]:      # repeat four times
    alex.forward(50)
    alex.left(90)

wn.exitonclick()

Benefits:

• simplified program - easier to understand

• found patterns of behaviour that can be reused

The range values, had nothing to do whith the loop number, anything could be inside:

for aColor in ["yellow", "red", "purple", "blue"]:      # repeat four times
    alex.forward(50)
    alex.left(90)

would work the same, plus the change of the color.

range function

for i in range(4):
    # Executes the body with i = 0, then 1, then 2, then 3
for x in range(10):
    # sets x to each of ... [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

a = range(1,5)            #range(start, stop)
print(a)
>>> [1,2,3,4]

b = range(2,9,2)        #range(start,stop,step)
print(b)
>>> [2,4,6,8]

c = print(range(10, 0, -1))
print(c)
>>> [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

Turtle specific methods

turtle.backward(-100) # will go forward
turtle.left(-30) #will turn right
turtle.up() /penup()
turtle.down() /pendown() # refers to up and down for pen drawing 
turtle.shape("turtle")
turtle.speed(10)
turtle.stamp() # stamp its inprint to canvas, not pen

Every turtle can have its own shape. The ones available “out of the box” are arrow, blank, circle, classic, square, triangle, turtle.

Method	Parameters	Description
Turtle	None	Creates and returns a new turtle object
forward	distance	Moves the turtle forward
backward	distance	Moves the turle backward
right	angle	Turns the turtle clockwise
left	angle	Turns the turtle counter clockwise
up	None	Picks up the turtles tail
down	None	Puts down the turtles tail
color	color name	Changes the color of the turtle’s tail
fillcolor	color name	Changes the color of the turtle will use to fill a polygon
heading	None	Returns the current heading
position	None	Returns the current position
goto	x,y	Move the turtle to position x,y
begin_fill	None	Remember the starting point for a filled polygon
end_fill	None	Close the polygon and fill with the current fill color
dot	None	Leave a dot at the current position
stamp	None	Leaves an impression of a turtle shape at the current location
shape	shapename	Should be ‘arrow’, ‘classic’, ‘turtle’, or ‘circle’

Turtle Docs

Modules

A module is a file containing Python definitions and statements intended for use in other Python programs. There are many Python modules that come with Python as part of the standard library.

• Global module index to find things

• Language reference

• Tutorial

The math and random modules

• Math module docs

The math module contains the kinds of mathematical functions you would typically find on your calculator and some mathematical constants like pi and e. As we noted above, when we import math, we create a reference to a module object that contains these elements.

import math

print(math.pi)
print(math.e)

print(math.sqrt(2.0))

print(math.sin(math.radians(90)))   # sin of 90 degrees

The random module:

• random.random()

• random.randrange()

import random

prob = random.random()
print(prob)

diceThrow = random.randrange(1, 7)       # return an int, one of 1,2,3,4,5,6
print(diceThrow)

>>> 0.885404889175
>>> 2

• pseudo-random since they depend on seed value