object oriented programming in python.ppt

object oriented programming in python.ppt

• 1.
  Python Mini-Course University ofOklahoma Department of Psychology Lesson 25 The object-oriented thought process 6/16/09 Python Mini-Course: Lesson 25 1
• 2.
  Lesson objectives 1. Definethe key terms used in object- oriented programming (OOP) 2. Understand the difference between an object and a class 3. Describe the types of relationships that are possible between objects 6/16/09 Python Mini-Course: Lesson 25 2
• 3.
  Procedural vs. OOP Reviewfrom Lesson 6 Procedural programming separates the program operations and the data Object-oriented programming packages the program operations and the data together in object 6/16/09 Python Mini-Course: Lesson 25 3
• 4.
  What is anobject? The building blocks of an O-O program A program that uses O-O is basically a collection of objects Objects interact much like things in the real world do 6/16/09 Python Mini-Course: Lesson 25 4
• 5.
  What is anobject? Objects have two components: Data (i.e., attributes) Behaviors (i.e., methods) 6/16/09 Python Mini-Course: Lesson 25 5
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  Object attributes Store thedata for that object Example (taxi): Driver OnDuty NumPassengers Location 6/16/09 Python Mini-Course: Lesson 25 6
• 7.
  Object methods Define thebehaviors for the object Example (taxi): PickUp DropOff GoOnDuty GoOffDuty 6/16/09 Python Mini-Course: Lesson 25 7 •GetDriver •SetDriver •GetNumPassengers
• 8.
  Object interface To usea method, the user (programmer) must know: Name of the method Parameters to pass to the method What (if anything) the method returns 6/16/09 Python Mini-Course: Lesson 25 8
• 9.
  Object implementation The userdoes NOT need to know how the method works internally 6/16/09 Python Mini-Course: Lesson 25 9
• 10.
  What is aClass? A blueprint for an object Classes can be thought of as templates or cookie cutters Given a class description, we can instantiate objects of that class Classes are high-level data types 6/16/09 Python Mini-Course: Lesson 25 10
• 11.
  OOP concepts Encapsulation Data andbehaviors are packaged together, but the object only reveals the interfaces needed to interact with it Internal data and behaviors can remain hidden 6/16/09 Python Mini-Course: Lesson 25 11
• 12.
  OOP concepts Interfaces Fundamental meansof communication between objects Should completely describe to user (programmer) how to interact with the object Should control access to attributes 6/16/09 Python Mini-Course: Lesson 25 12
• 13.
  Inheritance You can createnew classes by abstracting out common attributes and behaviors from a parent (or base) class 6/16/09 Python Mini-Course: Lesson 25 13
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  6/16/09 Python Mini-Course: Lesson25 14
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  Is-a relationship Because sub-classesinherit from their base class, they have an is- a relationship: Lion is a cat Cat is a mammal 6/16/09 Python Mini-Course: Lesson 25 15
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  Polymorphism Allows similar objectsto to respond to the same message (method call) in different manners Sub-classes can override base class methods 6/16/09 Python Mini-Course: Lesson 25 16
• 17.
  OOP example: animals.py classAnimal: def __init__(self, name): # Constructor of the class self.name = name class Cat(Animal): def talk(self): return 'Meow!' class Dog(Animal): def talk(self): return 'Woof! Woof!' 6/16/09 Python Mini-Course: Lesson 25 17
• 18.
  Composition Objects can containother objects This is called a has-a relationship Example:  Taxi has-a driver 6/16/09 Python Mini-Course: Lesson 25 18