CS21 In Class: week 5

objects and the graphics library

Setting up a subdirectory for week 5 in-class work

Thursday: If you copied over all of my week05 files already (Tuesday instructions below), then I want you to copy over a new version of the duplicate.py file (and enter y when cp asks if you want to overwrite it). Otherwise, follow Tuesday instructions: 
$ cd cs21/class/week05
$ pwd
$ cp ~newhall/public/cs21/week05/duplicate.py .
cp: overwrite './duplicate.py'? y
Tuesday: cd into your cs21/class/ subdirectory and create a new directory named 'week05', then cd into that directory: 
$ cd cs21/class                     # cd into your cs21/class subdirectory
$ pwd	          
  /home/your_user_name/cs21/class

$ mkdir week05                      # make a subdirectory named week05   
$ cd week05                         # cd into it
$ pwd           
  /home/your_user_name/cs21/class/week05

Now copy over all the files from my public/cs21/week05 directory into your week05 directory (remember to add the dot as the destination of the cp command). From your week05 directory: 

$ cp ~newhall/public/cs21/week05/* .
$ ls
animate.py   circleshift.py  partsmove.py     squares_list.py
bullseye.py  duplicate.py    randomcircle.py  test_graphics.py

Weekly In-class Examples

This week we are going to write some programs that manipulate objects. We will primarily be using the graphics library to create graphics objects that can be drawn into a graphics window.

The graphics library

To use the graphics library, first import it at the top of your program: 
  from graphics import *
Next create a new graphics window object, and then create gui objects to draw into this window: 
# creates new GraphWin object, 500x500 pixels in size
win = GraphWin("My GUI Program", 500, 500)   
# creates a new Circle object centered at 50,50 with a radius of 20 pixels
circ = Circle(Point(50,50), 20)    
# invoke the setFill method of the Circle object referred to by circ
circ.setFill("red")                
# draw the Circle object refered to by circ in GraphWin win
circ.draw(win)

Some more notes on using the Graphics library are available here: Graphics Library Reference. A link to this is also available in the References section at the bottom of the class webpage.

We are going to do some of the following together in class:
  1. open squares_list.py. We will complete the function from last week that takes a list of values and returns the square of the largest. We will also look at some examples of using the object interface to a list by creating a list of items using the append method.

  2. open test_graphics.py in vim. It contains some example code that draws different type objects to one of two graph windows. Let's try changing some things.

  3. open bullseye.py. Together we are going to write a program that draws a bullseye to the graphics window. It should consist of 4 concentric circles, of two or more colors, that are drawn centered in the graphics window.

  4. open randomcircle.py. Together we are going to write a function that draws some number of circles to random locations in the graphics window.

  5. Run colorPicker in the python interpreter to see the different available colors: 
    $ python
  from colorPicker import *
  colorPicker()

  6. open circle_shift.py. Try running it in python. Together we will change this program so that after first drawing the initial cirle, each time the user clicks on a new spot, the circle is shifted to the new location. The shifting will happen four times, and on the fifth mouse click the program will exit.

  7. open duplicate.py. We are going to try to use an existing Circle object as a starting point for creating a similar second Circle object. The attempt at doing this doesn't work. Let's think about why not and how to fix it.

  8. open animate.py. Let's look at this program together. Once we figure out what it is doing, lets change the code so that the animation will be repeated 3 times, each end point will be determined by the user's mouse click. If we want to repeat the same action multiple times, what language construct do we use? ...