Class Methods in Python: Understanding and Using Them Effectively

You have read about function, higher order function, closures etc. Now, it is time to learn about their scope. Based on the scope, functions/methods are of two types. They are:

• Class methods

• Static methods

Class Methods

Class Methods - Example

class Circle(object):
    no_of_circles = 0
    def __init__(self, radius):
        self.__radius = radius
        Circle.no_of_circles += 1
    def getCirclesCount(self):
        return Circle.no_of_circles
c1 = Circle(3.5)
c2 = Circle(5.2)
c3 = Circle(4.8)
print(c1.getCirclesCount())     # -> 3
print(c2.getCirclesCount())     # -> 3
print(Circle.getCirclesCount(c3)) # -> 3
print(Circle.getCirclesCount()) # -> TypeError

Class Methods - Example

3

3

3

TypeError: getCirclesCount() missing 1 required positional argument: 'self'

• In Example 1, getCirclesCount method is bound to objects of Circle.

• Hence when calling it,

  • on objects c1, and c2 resulted in 3.

  • on class Circle with object c3 as argument resulted in 3 again.

  • on class Circle without any object information resulted in TypeError.

Class Methods - Example

class Circle(object):
    no_of_circles = 0
    def __init__(self, radius):
        self.__radius = radius
        Circle.no_of_circles += 1
    @classmethod
    def getCirclesCount(self):
        return Circle.no_of_circles
c1 = Circle(3.5)
c2 = Circle(5.2)
c3 = Circle(4.8)

• In Example 2, getCirclesCount is decorated with classmethod.

• Thus making it a class method, which bounds to class Circle.

Class Methods - Example

print(c1.getCirclesCount())     # -> 3

print(c2.getCirclesCount())     # -> 3

print(Circle.getCirclesCount()) # -> 3

Output of Example 2

3

3

3

• In Example 2, class Circle is passed as argument to getCirclesCount in both cases. i.e when it is called on objects and the class.