Classes and objects | AI Pathshala

A class is a blueprint

classes.py

class Student:
    school = "AI Pathshala"             # Shared by every student

    def __init__(self, name, marks):    # Runs when a student is created
        self.name = name                # self means "this particular student"
        self.marks = marks

    def passed(self):
        return self.marks >= 40

riya = Student("Riya", 78)
aman = Student("Aman", 32)

print(riya.name, riya.passed())
print(aman.name, aman.passed())
print(riya.school)

Output

Riya True
Aman False
AI Pathshala

Inheritance and polymorphism

inheritance.py

class Animal:
    def __init__(self, name):
        self.name = name

    def speak(self):
        return "..."

class Dog(Animal):             # Dog gets everything Animal has
    def speak(self):           # And changes this part
        return "Woof"

class Puppy(Dog):
    def speak(self):
        return super().speak() + " (squeaky)"

for pet in [Animal("Generic"), Dog("Sheru"), Puppy("Tommy")]:
    print(pet.name, "says", pet.speak())

Output

Generic says ...
Sheru says Woof
Tommy says Woof (squeaky)

Magic methods and privacy

magic.py

class Basket:
    def __init__(self, items):
        self._items = items        # One underscore: "please don't touch directly"

    def __len__(self):             # Makes len(basket) work
        return len(self._items)

    def __str__(self):             # Makes print(basket) readable
        return "Basket with " + ", ".join(self._items)

    def __add__(self, other):      # Makes basket + basket work
        return Basket(self._items + other._items)

both = Basket(["apple"]) + Basket(["mango", "kiwi"])
print(both)
print(len(both))

Output

Basket with apple, mango, kiwi
3

Code challenge

Make a Rectangle class with width and height, and an area() method.

In __init__, store self.width and self.height. Then def area(self): return self.width * self.height.