Methods

Object Methods

• Methods called on objects have implicit first parameter

• … the object the method is called on

• Usually called self (not a must though; see Constructor)

class Person:
    def __init__(self, firstname, lastname):
        self.firstname = firstname
        self.lastname = lastname

    def say_hello(self, phrase):
        return f'{phrase} {self.firstname} {self.lastname}'

joerg = Person('Joerg', 'Faschingbauer')
joerg.say_hello("Howdy, I'm")

"Howdy, I'm Joerg Faschingbauer"

Class Methods (@classmethod)

• Not bound to an object

• Cannot be called on an object

• Rather, called on a class

• Implicit first parameter: the class object

• Usually named cls (again, not necessarily)

• Cool when inheriting/specializing Person

class Person:
    def __init__(self, firstname, lastname):
        self.firstname = firstname
        self.lastname = lastname

    @classmethod
    def make_child(cls, firstname, parent1, parent2):
        # ---- vvv --- not hardwiring class Person
        return cls(firstname, f'{parent1.lastname}-{parent2.lastname}')

mother = Person('Isolde', 'Haubentaucher')
father = Person('Joerg', 'Faschingbauer')

child = Person.make_child('Alex', mother, father)

Static Methods (@staticmethod)

• Like @classmethod

• Only without implicit parameter

• (Consequentially, does not play well with inheritance)

class Person:
    def __init__(self, firstname, lastname):
        self.firstname = firstname
        self.lastname = lastname

    @staticmethod
    def make_child(firstname, parent1, parent2):
        # ---- vvvvvv --- hardwiring class Person
        return Person(firstname, f'{parent1.lastname}-{parent2.lastname}')

• Used the same as classmethod

mother = Person('Isolde', 'Haubentaucher')
father = Person('Joerg', 'Faschingbauer')

child = Person.make_child('Alex', mother, father)