Methods

A method is a function defined inside a class. It works on one object — the object it is called on, available in the body as self:

class Rectangle:
    def __init__(self, width, height):
        self.width = width
        self.height = height

    def area(self):
        return self.width * self.height

    def is_square(self):
        return self.width == self.height

Methods are called with a dot, like the list and string methods you have used all course — those were methods of exactly this kind:

r = Rectangle(3, 4)
print(r.area())
print(r.is_square())

Output:

12
False

r.area() runs area with self set to r, so self.width is 3. Every method's first parameter is self; the call site never passes it.

The difference from a plain function: area(r) would need the rectangle handed to it, while r.area() belongs to the object — data and the operations on that data live together in one definition.

Exercise

Extend the Movie class from the previous lesson.

1. __init__ stores title, year, and runtime, as before.
2. Add a method named is_long that returns True when runtime is over 120 minutes.
3. Add a method named age_in with one parameter, current_year. It returns how many years old the movie is in that year.

Movie("Alien", 1979, 117).age_in(2026) returns 47.

Run your code to see the output, then press Submit.

Tests

import unittest


class TestMovieMethods(unittest.TestCase):
    def test_117_minutes_is_not_long(self):
        self.assertIs(Movie("Alien", 1979, 117).is_long(), False)

    def test_121_minutes_is_long(self):
        self.assertIs(Movie("Solaris", 1972, 167).is_long(), True)

    def test_exactly_120_minutes_is_not_long(self):
        self.assertIs(Movie("X", 2000, 120).is_long(), False)

    def test_age_in_2026(self):
        self.assertEqual(Movie("Alien", 1979, 117).age_in(2026), 47)

    def test_age_in_release_year_is_zero(self):
        self.assertEqual(Movie("Alien", 1979, 117).age_in(1979), 0)