Creating and initialising a Class in Python

To create an instance of a class ("to instantiate it") do

myObject = ClassName()

Where ClassName is the name of the class for which you want to create a new object. myObject will be an object of type ClassName.

A class instance is often instantiated by passing parameters whose values are determined when the program is run. The values passed in as parameters are typically used by the functions in the class.

 # Passing in a parameter when instantiating an object    
myObject = ClassName("A value")

Python uses the special function name __init__ for constructing a class with parameters. This function always takes self as the first parameter because the class constructor needs to know its own instance, just like the class' functions.

class Animal():
    def __init__(self, animal):
        self.animal = animal;

    def speak(self):
        if self.animal == 'Dog':

        if self.animal == 'Cat':

animal1 = Animal('Dog')

animal2 = Animal('Cat')



The self Parameter

Notice that the definition of speak has self as a parameter, but when we call speak we don't pass in self. The Python inprepretor will always (quietly, in the background) pass a reference to the object that called the function, to the function. This means speak will have animal1 (for example) passed into the method, and animal1 can be accessed via the self parameter. Read more about self.