Methods

A method is a function defined inside a class, and it works on the object it is called on through self.

Last updated: 30 Sep, 2026 · Python 3.14

The Ticket class from Classes holds data but does nothing. Methods give it actions.

class Car:
    def __init__(self, window, door, enginetype):
        self.windows = window
        self.doors = door
        self.enginetype = enginetype

    def self_driving(self):
        return f"This is a {self.enginetype} car"

car1 = Car(4, 5, "petrol")
print(car1.self_driving)
print(car1.self_driving())

<bound method Car.self_driving of <__main__.Car object at 0x106588ec0>>
This is a petrol car

Without brackets, car1.self_driving is the method itself, printed as a bound method with a memory address. With brackets it runs, and self.enginetype reads this car's engine type. The Ticket class below gets a method the same way.

Syntax:

class Name:
    def action(self):
        ...            # self is the object the method was called on

obj.action()

Adding a categorise method

class Ticket:
    def __init__(self, ticket_id, customer, text):
        self.id = ticket_id
        self.customer = customer
        self.text = text
        self.category = None

    def categorise(self):
        text = self.text.lower()
        if "charged" in text or "refund" in text:
            self.category = "billing"
        elif "parcel" in text or "arrived" in text:
            self.category = "shipping"
        else:
            self.category = "other"

ticket = Ticket(1, "Asha", "I was charged twice for one order")
print(ticket.category)
ticket.categorise()
print(ticket.category)

None
billing

__init__ now starts every ticket with category set to None. categorise is a method: def inside the class, with self first.

ticket.categorise() passes ticket in as self, so self.text is this ticket's text and setting self.category changes this ticket. It is the categorise function from Functions, now keeping its answer on the object.

Adding a method that returns

    def summary(self):
        return f"#{self.id} {self.customer}: {self.category}"

tickets = [
    Ticket(1, "Asha", "I was charged twice for one order"),
    Ticket(2, "Ben", "My parcel has not arrived"),
]
for ticket in tickets:
    ticket.categorise()
    print(ticket.summary())

#1 Asha: billing
#2 Ben: shipping

A list of objects works like the list of dictionaries in Lists of dictionaries, and each one knows how to sort and describe itself.

Forgetting self

class Ticket:
    def __init__(self, text):
        self.text = text

    def shout():
        return "TICKET"

Ticket("refund").shout()

Traceback (most recent call last):
  File "main.py", line 8, in <module>
    Ticket("refund").shout()
TypeError: Ticket.shout() takes 0 positional arguments but 1 was given

Python always passes the object as the first argument to a method. A method written without a parameter for it receives one argument it has no room for.

A function vs a method

Where methods show up in AI code

• Most framework calls are methods: client.chat.completions.create(...), agent.invoke(...).
• Keeping the steps that belong to one record, such as a ticket, next to its data.

Related

• Previous: Classes
• Next: dataclasses
• Reference: Method Objects in the Python tutorial