Object-Oriented Programming

Classes and Instances

• Class: A bundle of data and functionality. This can be copied and modified to accomplish a wide variety of programming tasks.

  • A blueprint on how to build an object

  • Class names begin with capital letters

    • classes with multiple words should be UpperCamelCase

• Instance: a specific working copy of a class. Also referred to as an object. it is an individual object produced from the class.

class NewDog:    #This is the class we created
    pass

fido = NewDog()     #fido and snoopy are individual instances
snoopy = NewDog()    #of the NewDog class

Building Your Own Instance Methods/Functions

• If you place a function within the body of a class, that function becomes a specific method for the instances of that class

• It is convention to create each class inside its own file in python

•   class Dog:
        def bark(self):
            print("Woof!")
  
    fido = Dog()  #The instance is created
    fido.bark()    #To call the function, use dot notation 
    #Woof!
  

Understanding (__init__)

• everytime we initialize a new object, the python interpreter calls a magic method called init.

  • The magic methods are special methods that are not meant to be called by developers but are invoked by different cues and operators that act on the object.

  • It is invoked when you initialize a class

  • You can overwrite init to change an object's behavior

  • It can be modified to take more arguments to customize the behavior of unique objects

  •   class Dog:
          def __init__(self, name):
              print(f"{name} is born")
    
          def bark(self):
              print("Woof!")
    
      fido = Dog()  
      #Fido is born   This happens automatically
      fido.bark()
      #Woof!
    

• Understanding Self

  • self is a reference to the initialized object. It is used to make the instance more unique

•   class Dog:
        def __init__(self, name):
            self.name = name
  
        def bark(self):
            print("Woof!")
  
    fido = Dog("Fido")
    fido.name
    #Fido
  

Attributes and Properties

• Attribute: Variables that belong to an object

• Class Attributes: set outside the scope of any methods

• Instance Attributes: varies from 1 instance to the next

• You can set/change/add/and retrieve attributes suing dot notation

• Pyhton also has a few built-in functions to manipulate attributes

  • getattr(): retrieves the value of an attribute

  • setattrs(): changes the value of an attribute

  • hasattr(): checks for the presence of the attribute

  • delattr(): removes an attribute from a class or object

• Properties: Used when we need to make sure an attribute meets a certain set of criteria. These are controlled by methods