Python Projects for Beginners a ten-Week Bootcamp Approach to Python Programming

The “self” Keyword

The self keyword is a reference to the current instance of the class and is used to access variables and methods associated with that instance. Think about a soccer team you’ve never seen play before. How do you distinguish each player from the next? You would probably use the numbers on the back of their jerseys. Even though each player is a person with different features, it’s easy for you to pick out any of them based on their number. In Python, it’s essentially how objects that are created from the same source are identified. In the previous cell, we printed out the attribute color from the ford instance. The reason Python knew where to access this value, specifically for ford, is because we used the self keyword. We didn’t need it for basic classes because those attributes were globally accessible, which will be covered later today. For now, just know that when you want to instantiate an object with personalized attributes, you need to have the init method declared and use the self keyword to save each attributes value.

Instantiating Multiple Objects with __init__( )

To truly understand how the init method works, let’s instantiate a couple instances with two attributes of different values:

# defining different values for multiple instances class Car( ):
def __init__(self, color, year):
self.color = color # sets the attribute color to the value passed in
self.year = year
ford = Car("blue", 2016) # create a car object with the color blue and year 2016
subaru = Car("red", 2018) # create a car object with the color red and year 2018
print(ford.color, ford.year) print(subaru.color, subaru.year)

Go ahead and run the cell. The two print statements at the bottom will output each instance’s attributes. When we instantiated the ford and subaru objects, we gave them different values for each of their respective attributes. This is the beauty of OOP. We’re able to build two different objects from the same source using just two lines. Even if the class itself was thousands of lines long, to create ten different instances would only take ten lines of code.