Class attribute, @classmethod, @staticmethod

Class method, class attribute, instance method, instance attribute, static method

Class method takes cls as the first parameter, it can access or modify the class state
Static method needs no specific parameters, it can't access or modify class or instance state

When to use class method?

As a factory, delicious pizza factories with @classmethod

Example

class Dog:
	num_legs = 4 # <- Class variable
	def __init__(self, name):
		self.name = name # <- Instance variable


>>> jack = Dog('Jack') 
>>> jill = Dog('Jill') 
>>> jack.name, jill.name 
('Jack', 'Jill')
>>> jack.num_legs, jill.num_legs 
(4, 4)
>>> Dog.num_legs
4

>>> Dog.num_legs = 6
>>> jack.num_legs, jill.num_legs 
(6, 6)
>>> Dog.num_legs = 4 
>>> jack.num_legs = 6
>>> jack.num_legs, jill.num_legs, Dog.num_legs 
(6, 4, 4) # 6 -> now num_legs is instance attribute for jack
>>> jack.num_legs, jack.__class__.num_legs 
(6, 4) # now the new num_legs instance variable “shadows” the class variable of the same name, overriding and hiding it when we access the object instance scope

# Number of instance 
class CountedObject: 
	num_instances = 0
	def __init__(self): 
		self.__class__.num_instances += 1

>>> CountedObject.num_instances 0
>>> CountedObject().num_instances 1
>>> CountedObject().num_instances 2
>>> CountedObject().num_instances 3
>>> CountedObject.num_instances 3

Class attribute, @classmethod, @staticmethod

Class method, class attribute, instance method, instance attribute, static method

Example

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