Methods and self

Attributes are the data an object holds. Methods are the things an object can do. A method is just a function defined inside a class, and like __init__ its first parameter is self so it can read and change the object's own data.

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

    def increment(self):
        self.count = self.count + 1

    def value(self):
        return self.count

c = Counter()
c.increment()
c.increment()
print(c.value())   # 2

You call a method with a dot, the same way you read an attribute, but with parentheses: c.increment(). Again you do not pass self, Python passes the object on the left of the dot in for you.

Methods can take extra parameters too, and they can use other attributes on self:

class Greeter:
    def __init__(self, greeting):
        self.greeting = greeting

    def greet(self, name):
        return f"{self.greeting}, {name}!"

g = Greeter("Hi")
print(g.greet("Sam"))   # Hi, Sam!

A method that returns a value uses return, just like a normal function.