Classes, Objects & Constructors

Lesson 1 · OKSTEM College · Associate of Science in Computer Science

Classes, Objects & Constructors

A class is a blueprint; an object is a concrete instance created from that blueprint. Python's __init__ method is the constructor — it runs automatically when a new object is created.

class Student:
    """A student at OKSTEM College."""

    def __init__(self, name: str, gpa: float):
        self.name = name          # instance variable
        self.gpa  = gpa
        self.courses: list = []

    def enroll(self, course: str) -> None:
        self.courses.append(course)

    def __repr__(self) -> str:
        return f"Student({'{'}self.name!r{'}'}, gpa={'{'}self.gpa{'}'})"

# Usage
alice = Student("Alice", 3.9)
alice.enroll("CS 201")
print(alice.courses)   # ['CS 201']
print(repr(alice))     # Student('Alice', gpa=3.9)

Every method's first parameter is self — a reference to the instance. Python passes it automatically; you never pass it explicitly when calling a method.

Knowledge Check

The __init__ method is called

'self' in a Python method refers to

Instance variables are set on

Which method controls how an object is displayed with repr()?

A class is best described as