classmethods tutorial python code example

Example 1: python: @classmethod

class Float:
    def __init__(self, amount):
        self.amount = amount

    def __repr__(self):
        return f'<Float {self.amount:.3f}>'

    @classmethod
    def from_sum(cls, value_1, value_2):
        return cls(value_1 + value_2)


class Dollar(Float):
    def __init__(self, amount):
        super().__init__(amount)
        self.symbol = '€'

    def __repr__(self):
        return f'<Euro {self.symbol}{self.amount:.2f}>'


print(Dollar.from_sum(1.34653, 2.49573))

Example 2: python classmethod

class point:
	def __init__(self, x, y):
    	self.x = x
        self.y = y
        
    @classmethod
    def zero(cls):
    	return cls(0, 0)
        
    def print(self):
    	print(f"x: {self.x}, y: {self.y}")
        
p1 = point(1, 2)
p2 = point().zero()
print(p1.print())
print(p2.print())

Example 3: python classmethod

# classmethod example
In [20]: class MyClass:
    ...:     @classmethod
    ...:     def set_att(cls, value):
    ...:         cls.att = value
    ...:

In [21]: MyClass.set_att(1)

In [22]: MyClass.att
Out[22]: 1

In [23]: obj = MyClass()

In [24]: obj.att
Out[24]: 1

In [25]: obj.set_att(3)

In [26]: obj.att
Out[26]: 3

In [27]: MyClass.att
Out[27]: 3