Introduction to Python Class¶

Creating Classes¶

Look the code below. It defines a class. it also declares methods which are functions that are defined inside of a class. One of the methods, __init__, is automatically called when a new object is created by the class. One of the methods, __str__, is automatically called when you print an object of the class. These methods start and end with two underscores.

Run the following code

Creating More Objects¶

Once you have defined a class you can use it to create many objects.

Change the following main function to add a new person object.

Add a Method to a Class¶

You can add a new method to a class by adding a new function inside the class. For example, you can add the initials method to the Person class. The name of the function doesn’t need to have any underscores in it. It only needs to start and end with double underscores if it is a special method like __init__ or __str__. It does need to take the current object which is by convention referred to as self.

The following Person class has an initials method that returns a string with the first letter in the first name and the first letter in the last name in lowercase.

class Person:
    """ Represents a person object """

# initializes the values in a new object called self
    def __init__(self, first, last):
        self.first = first # set first in self to the passed first
        self.last = last   # set last in self to the passed last

# returns a string with information about the object self
    def __str__(self):
        return self.first + " " + self.last

# returns the first characters of the first and last name in lowercase
    def initials(self):
        return self.first[0].lower() + self.last[0].lower()

def main():
    # calls the __init__ method
    p1 = Person("Barbara", "Ericson")

# calls the __str__ method
    print(p1)

# calls the initials method
    print(p1.initials())

main()

====
from unittest.gui import TestCaseGui
class myTests(TestCaseGui):

def testOne(self):
        p1 = Person("Barbara", "Ericson")
        self.assertEqual(p1.initials(),'be',"testing initials for Barbara Ericson")
        p2 = Person("Enoch", "Obe")
        self.assertEqual(p2.initials(),"eo", "testing initials for Enoch Obe")

myTests().main()

Glossary¶

class: A template that can be used to construct an object. Defines the attributes and methods that will make up the object.
attribute: A variable that is part of a class.
constructor: An optional specially named method ( __init__ ) that is called at the moment when a class is being used to construct an object. Usually this is used to set up initial values for the object.
inheritance: When we create a new class (child) by extending an existing class (parent). The child class has all the attributes and methods of the parent class plus additional attributes and methods defined by the child class.
method: A function that is contained within a class and the objects that are constructed from the class. Some object-oriented patterns use ‘message’ instead of ‘method’ to describe this concept.

What to do next¶

Click to see an introduction about our system 👉 System Introduction

You have attempted of activities on this page