I210 review (for final exam) Fall 2011, IUB

1. I210 review(for final exam)Fall 2011, IUB

2. What’s in the Final Exam • Multiple Choice (5) • Short Answer (5) • Program Completion (3) • Note: A single-sidedA4 cheat-sheet is allowed; write your name and ID on the cheat-sheet; and turn in your cheat-sheet together with the final exam.

3. Basics • Variables • Data types • list • conversion • Branching structures • Loops (while & for loops) • Functions • Function header • Return values • Parameters and arguments

4. Understanding OOP • OOP allows representation of real-life objects as software objects (e.g., a dictionary as an object) • Object: A single software unit that combines attributes and methods • Attribute: A "characteristic" of an object; like a variable associated with a kind of object • Method: A "behavior" of an object; like a function associated with a kind of object • Class: Code that defines the attributes and methods of a kind of object (A class is a collection of variables and functions working with these variables)

5. Creating Classes for Objects class Puppy(object): def __init__(self, name, color): self.name = name self.color = color def bark(self): print "I am", self.color, self.name puppy1 = Puppy("Max", "brown") puppy1.bark() puppy2 = Puppy("Ruby", "black") puppy2.bark() • Class: Code that defines the attributes and methods of a kind of object • Instantiate: To create an object; A single object is called an Instance

6. Special Methods def __init__(self): print "A new critter has been born!” #Constructor, __init__() #Automatically called by new Puppy object def __str__(self): rep = "Critter object\n" rep += "name: " + self.name + "\n" return rep # __str__() # return a string

7. Private vs Public Attributes and Methods • Public:Can be directly accessed by client code • Private:Cannot be directly accessed (easily) by client code • By default, all attributes and methods are public • But, can define an attribute or method as private class Critter(object): def __init__(self, name, mood): self.name = name # public self.__mood = mood # private

8. Understanding Inheritance • Inheritance: An element of OOP that allows a new class to be based on an existing one where the new automatically gets (or inherits) all of the methods and attributes of the existing class • The children classes get all the capabilities (methods) and properties (attributes) the parent class has; the children classes are also called derived classes • Get the code for free! (code-reuse) – inheritance allows a new class to re-use code which already existed in another class (the parent class)

9. Derived Classes are New Classes • To create specializations of existing classes or objects by adding new attributes and methods! • often called subtyping when applied to classes. In specialization, the new class or object has data or behavior aspects that are not part of the inherited class. • Overriding (e.g., over-ridding of the + operator, so + has different meaning, addition of two numbers, concatenation of two strings, etc) – the same method that does something different Guide to Programming with Python

10. Altering the Behavior of Inherited Methods: Overriding • Override: To redefine how inherited method of base class works in derived class • Two choices when overriding • Completely new functionality • Incorporate functionality of overridden method, add more • How to invoke base class’ methods?

11. Inheritance Example: Animal Class class Animal(object): def __init__(self, name): # Constructor self.name = name def get_name(self): return self.name class Cat(Animal): def talk(self): return 'Meow!' class Dog(Animal): def talk(self): return 'Woof! Woof!' animals = [Cat('Missy'), Cat('Mr. Bojangles'), Dog('Lassie')] for animal in animals: print animal.talk() + ' I am ' + animal.get_name() Base class: A class upon which another is based; it is inherited from by a derived class Derived (child) class: A class that is based upon another class; it inherits from a base class

12. Understanding Event-Driven Programming • Event-driven program: A program that responds to actions regardless of the order in which they occur (vs structured programming) • Event: Something that happens involving a program's objects (mouse moves over; click of a button, etc) • Event handler: Code that runs when a specific event occurs • Bind: To associate an event with an event handler • Event loop: A loop that checks for events and calls appropriate event handlers when they occur • GUI programs traditionally event-driven: the users control the flow of the program

13. Buttons on Strike (I) from Tkinter import * root = Tk() #a root window, upon which other GUI elements can be added root.title("Simple GUI Demo") #add title root.geometry("400x200") #change the size of the window app = Frame(root) #create a frame, upon which other Widgets can be added app.grid() #need to invoke grid() method button = Button(app, text = "I am button #1”) button.configure(text = "I am button #2”) button['text'] = "I am button #3” button["command"] = update_count button.grid() root.mainloop() #must start up the window's event loop!!! (II) (III) (IV)

14. Writing a Game Using Pygame & Livewires #(1) Import pygame or livewires from livewires import games #(2) Create a graphical window games.init(screen_width = 640, screen_height = 480, fps = 50) #(3) Start up window’s main loop games.screen.mainloop()

15. Understanding the Graphics Coordinate System • Graphics screen made up of rows and columns of pixels • Specify point on screen with coordinates: x and y ; Upper-leftmost pixel is (0,0) • Can place graphics objects on screen using coordinate system screen.width screen.height

16. Control a Sprite Sprite: A graphics object with an image class Pizza(games.Sprite): """ A bouncing pizza. """ def update(self): if games.keyboard.is_pressed(games.K_UP): self.x -= 1 if self.right > games.screen.width or self.left < 0: self.dx = -self.dx if self.bottom > games.screen.height or self.top < 0: self.dy = -self.dy

17. Sample Question 1 • In Pygame, what is a sprite? What is a sprite collision?

18. Sample Question 2 • Complete the following GUI code that creates a button… from ____________ import * class Application(Frame): def __init__(self, master): Frame.__init__(self, master) self.grid() ___________________________ self.create_widget() defcreate_widget(self): self.lbl = Label(self, text="Click to increment!") ________________________ self.bttn = Button(self) ...