Methods

Fatma Kahveci
Coding
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Instance methods

  • The basic no-frills method
  • It takes one parameter, self.
    • self points to an instance of <Class> when the method is called.
    • You can freely access attributes and other methods on the same object with self.
class Pizza:
    def __init__(self, ingredients):
        self.ingredients = ingredients

    def __repr__(self):
        return f'Pizza({self.ingredients!r})'

Pizza(['cheese', 'tomatoes']) # Pizza(['cheese', 'tomatoes'])

Magic methods

  • def __str__(self): is a magic method.
def __add__(self, other):
 return self.pay + other.pay

def __len__(self):
 return len(self.name)

Special Methods

from math import hypot

class Vector:

  def __init__(self, x=0, y=0):
    self.x = x
    self.y = y

  def __repr__(self):
    return 'Vector(%r, %r)' % (self.x, self.y)

  def __abs__(self):
    return hypot(self.x, self.y)

  def __bool__(self):
    return(bool(abs(self)))

  def __add__(self, other):
    x = self.x + other.x
    y = self.y + other.y
    return Vector(x, y)
  
  def __mul__(self, scalar):
    return Vector(self.x * scalar, self.y * scalar)
  • They are called by the Python interpreter.
  • If my_object is an instance of a user-defined class, then Python calls the __len__ instance method you implemented.
    • Do not write my_object.__len__()
    • Write len(my_object)

Static methods

  • It takes neither a self nor a cls parameter.
  • It can neither modify object state nor class state.
import math

class Pizza:
    def __init__(self, radius, ingredients):
        self.radius = radius
        self.ingredients = ingredients

    def __repr__(self):
        return (f'Pizza({self.radius!r}, '
                f'{self.ingredients!r})')

    def area(self):
        return self.circle_area(self.radius)

    @staticmethod
    def circle_area(r):
        return r ** 2 * math.pi

p = Pizza(4, ['mozzarella', 'tomatoes'])
p # Pizza(4, ['mozzarella', 'tomatoes'])
p.area() # 50.26548245743669
Pizza.circle_area(4) # 50.26548245743669