Override Magic Methods

Making Objects Printable

class Employee: 
    def __init__(self, name, age, id): 
        self.name = name 
        self.age = age
        self.id = id 

employeeObject = Employee('employeeName', 20, 1101)

print(employeeObject)

Outputs

<__main__.Employee object at 0x000001DBB695FB50>

This occurs because we did not code a behaviour for our objects when they are used in String Scenarios. We must override two functions: str() and repr().

To make an object printable.

We must override two built-in base functions in Python:

1. __str__()

2. __repr__()

The __str__() method returns a human-readable, or informal, string representation of an object. Often called when the object is within a print() or str()

The __repr__() method returns a more information-rich, or official, string representation of an object. This is often called when your custom object needs to be displayed within another or any other sitution where __str__() is not used.

Fixing out classes

class Employee: 
    def __init__(self, name, age, id): 
        self.name = name 
        self.age = age
        self.id = id 
    
    def __str__(self):
        return f"{self.id}: {self.name}"
    
    def __repr__(self):
        return f'Employee(name = {self.name}, age = {self.age}, id = {self.id})'

employeeObject = Employee('employeeName', 20, 1101)

print(employeeObject)
print(repr(employeeObject))

Outputs:

1101: employeeName
Employee(name = employeeName, age = 20, id = 1101)

Other Base Functions to Override.

Addition, Subtraction, Multiplication, Division

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    
    def __add__(self, other_point):
        return Point(self.x + other_point.x, self.y + other_point.y)

    def __str__(self):
        return f"Point({self.x}, {self.y})"

p1 = Point(1,2)
p2 = Point(3,4)
p3 = p1 + p2 # This is possible due to the override of __add__()
print(p3) # Outputs Point(4,6)

The built-in arithmetic operators can be overridden to allow your custom class objects to interact with them. The subtraction, multiplication, and division operators will be overridden similar to the addition method above.

__add__() --> addition operator (+)
__sub__() --> addition operator (-)
__mul__() --> addition operator (*)
__div__() --> addition operator (/)

Contain - The in operator

// Some code

TBC