Class anatomy: attributes and methods

Object-Oriented Programming in Python

Alex Yarosh

Content Quality Analyst @ DataCamp

A basic class

class Customer:

    # code for class goes here

    pass

class <name>: starts a class definition
code inside class is indented
use pass to create an "empty" class

c1 = Customer()
c2 = Customer()

use ClassName() to create an object of class ClassName

Add methods to a class

class Customer:  

    def identify(self, name):   
      print("I am Customer " + name)

method definition = function definition within class
use self as the 1st argument in method definition

cust = Customer()
cust.identify("Laura")

I am Customer Laura

ignore self when calling method on an object

class Customer:  

    def identify(self, name):   
      print("I am Customer " + name)

cust = Customer()
cust.identify("Laura")

What is self?

classes are templates, how to refer data of a particular object?
self is a stand-in for a particular object used in class definition
should be the first argument of any method
Python will take care of self when method called from an object:

cust.identify("Laura") will be interpreted as Customer.identify(cust, "Laura")

We need attributes

Encapsulation: bundling data with methods that operate on data
E.g. Customer's' name should be an attribute

$$\text{\Large{Attributes are created by assignment (=) in methods}}$$

Add an attribute to class

class Customer:  
    # set the name attribute of an object to new_name
    def set_name(self, new_name):

      # Create an attribute by assigning a value
      self.name = new_name          # <-- will create .name when set_name is called

cust = Customer()                   # <--.name doesn't exist here yet

cust.set_name("Lara de Silva")      # <--.name is created and set to "Lara de Silva"

print(cust.name)                    # <--.name can be used

Lara de Silva

Old version

class Customer:  



    # Using a parameter
    def identify(self, name):   
      print("I am Customer" + name)

cust = Customer()

cust.identify("Eris Odoro")

I am Customer Eris Odoro

New version

class Customer:  
   def set_name(self, new_name): 
      self.name = new_name

    # Using .name from the object it*self*
    def identify(self):     
      print("I am Customer" + self.name)

cust = Customer()
cust.set_name("Rashid Volkov")
cust.identify()

I am Customer Rashid Volkov

Let's practice!

Object-Oriented Programming in Python