A class is a type you define. An object is one instance. self is that instance inside a method. This is a light pass — enough to read and write a small class.

Goal

Define __init__, a method, and two instances.

A record with behavior

class Student:
    def __init__(self, name, score):
        self.name = name
        self.score = score

    def passed(self, mark=90):
        return self.score >= mark

    def label(self):
        return f"{self.name}: {self.score}"

ada = Student("Ada", 98)
alan = Student("Alan", 88)
print(ada.label())
print(ada.passed(), alan.passed())
print(ada.name, ada.score)

__init__ runs on Student(...). Attributes live on self.

Methods vs functions

class Counter:
    def __init__(self):
        self.n = 0

    def bump(self, step=1):
        self.n += step
        return self.n

c = Counter()
print(c.bump())
print(c.bump(4))
print(c.n)

`str`

class City:
    def __init__(self, name, region):
        self.name = name
        self.region = region

    def __str__(self):
        return f"{self.name} ({self.region})"

print(City("Nairobi", "Central"))
print(City("Mombasa", "Coast"))

Without __str__, print shows a default <City object ...>.

Tip

Start with dicts and functions. Promote to a class when several functions all take the same bundle of fields.