Tue Sep 17

First let's go over the homework.

Questions?

My solutions are in code/homework/sep17.

(You can put ?html at the end of a url to see color coded code.)

So far we know about

• creating & running python programs
• reading in and printing out strings and numbers
• putting values of various types into variables
• using "import" to get other libraries like math ("modules")
• using dir() to see the defined variable names at the top level and in a module

Next : starting to understand the notion of an "object".

chap 4 - objects and graphics

This is usually a fun week ...

objects

Object oriented programming is a popular paradigm these days. It's not the only one, but it's an important one.

An "object" is a abstration chunk of data (a "thing") with actions (called "methods") it can perform.

A "class" is a kind of object. Example: Point, Circle, GraphWin

An "instance" is a specific object: Example: that red circle right there.

In python, creating an instance is done this way :

p = Point(10, 20)  # instance_variable = ClassName(argument1, arg2) 

And once we have one, we can tell it do things like this:

 p.move(2, 3)       # change position (x,y)=(10,20) to (12,23) 

An "API" (Application Programmer's Interface) is a description of which sorts of objects you can create, and what methods they have.

All this is pretty abstract, so let's see a concrete example with the attached files.

graphics.py

See the resources page or check out the web page for Zelle's textbook for both (1) the file you'll need to run this stuff (put in in the same directory), and (2) the API of what you can do with it.

• graphics.py
• Zelle's Graphics Module API

It's possible that your python installation doesn't yet have the right system stuff - namely tkinter - to run Zelle's graphics library. So if this doesn't work for you we'll need to play around a bit.

You'll need the graphics.py module (i.e. file) from Zelle. And it needs to be somewhere where your python can find it, typically in the same folder as the python file you're running.

If you're using IDLE, then you need to get it to the same folder as the graphics.py file. One way to do that is store a .py file of your own in that folder, then open that file.

# You'll need to do this to use Zelle's graphics:
from graphics import *

# If that doesn't work, make sure you have his graphics.py file.
# Then make sure you're running python in the folder with graphics.py.
# You can see what the folder is with :
import os
print "The current directory is ", os.getcwd()

# And you can change the folder with
os.chdir(full_path_to_a_folder)

With that stuff running, we'll explore it interactively class, doing things like this :

• create a window
  • with given size
  • with given background
• create a circle
  • give it a color
  • draw it
  • move it
  • animate it
    • "from time import sleep"
    • "import random; r = Random(); r.randint(low,high)"
• get a mouse click
• draw an image from a .jpeg file

... and so on

Tic Tac Toe, anyone ?

an example

# wiggle.py
#
# a demo of Zelle's graphic library
#
#  new python functions:
#
#     from random import randint
#     randint(low, high)   low <= random num <= high
#
#     from time import sleep
#     sleep(2)             do nothing for 2 sec
#
# Jim M | Sep 2012 | MIT License

from graphics import *
from time import sleep
from random import randint

def main():
    window = GraphWin("wiggle", 300, 300)
    dot = Circle(Point(150,150), 20)
    dot.setFill("red")
    dot.draw(window)
    for i in range(100):
        dx = randint(-5, 5) # pixels
        dy = randint(-5, 5)
        dot.move(dx, dy)
        sleep(0.1)  # in seconds
    wait = window.getMouse()

main()

aside : color

Discuss the model of color that computers use :

• additive (light) not pigment (paint)
• why 3 primary colors?
• corners of color cube
• 1 byte per color, i.e. a number (0 to 255) in base 10 or (00 to FF) in hex.
• go through the names for each corner of the "color cube"
• https://en.wikipedia.org/wiki/RGB_color_model
• https://en.wikipedia.org/wiki/Web_colors
• http://htmlcolorcodes.com/
• Color names : http://www.w3schools.com/html/html_colornames.asp

practice in class

If there's time :

• Modify the wiggle.py to show brownian motion, jiggling a point and drawing a line behind it.
• Draw rectangles showing ascii colors
• Draw a spiral
• Draw a math function like y = x**2

We wrote a short program to generate a grid of colors.

"""                                                                                      
 colorgrid !!!                                                                           
"""
from graphics import *

def main():
    window_width = 500
    cell_width = 10
    red = 100
    window = GraphWin("colorgrid", window_width, window_width)
    for x in range(0, window_width, cell_width):
        for y in range(0, window_width, cell_width):
            rect = Rectangle(Point(x, y), Point(x + cell_width, y + cell_width))
            green = int(255*(x/window_width))
            blue = int(255*(y/window_width))
            color = color_rgb(red, green, blue)
            rect.setFill(color)
            # TODO: try setting the outline to the same color with setOutline            
            rect.draw(window)
    wait = window.getMouse()

main()

attachments

		last modified	size
	screenshot.png	Fri Apr 26 2024 01:04 am	226K