Class Variables

Class variables are those variables which doesn’t belong objects, i.e they are class specific variables and they are shared among objects.

class Employee:

    raise_amount = 1.04

    def __init__(self, first_name, last_name, salary):
        self.first = first_name
        self.last = last_name
        self.pay = salary
        self.email = "{}.{}@company.com".format(first_name, last_name)

    def full_name(self):
        return "{} {}".format(self.first,self.last)

    def apply_raise(self):
        self.pay = int(self.raise_amount * self.pay)

emp1 = Employee("Harvey", "Specter", 1000000)
emp2 = Employee("Donna", "Paulson", 1000000)

print("===== OBJECT ATTRIBUTES =====")

print(emp1.pay)
emp1.apply_raise()
print(emp1.pay)

OUTPUT :

===== OBJECT ATTRIBUTES =====
1000000
1040000

1. Class variables are initialised in class without self.

2. We can access the value of class variable using class name or self.

   If we try to modify the class variable outside the class by accessing object name then it will not modify the class variable in fact it will actually create a new object specific attribute

Let’s check this using namespace

class Employee:

    raise_amount = 1.04

    def __init__(self, first_name, last_name, salary):
        self.first = first_name
        self.last = last_name
        self.pay = salary
        self.email = "{}.{}@company.com".format(first_name, last_name)

    def full_name(self):
        return "{} {}".format(self.first,self.last)

    def apply_raise(self):
        self.pay = int(Employee.raise_amount * self.pay)

emp1 = Employee("Harvey", "Specter", 1000000)
emp2 = Employee("Donna", "Paulson", 1000000)



print('===== NAMESPACE ========')
print(Employee.__dict__)
print('')
print(emp1.__dict__)

emp1.raise_amount = 2

print('\n===== NAMESPACE AFTER MODIFICATION ========\n')
print(Employee.__dict__)
print('--------------------------')
print(emp1.__dict__)

OUTPUT :


===== NAMESPACE ========
{'__module__': '__main__', 'raise_amount': 1.04, '__init__': <function Employee.__init__ at 0x7f859cef6620>, 'full_name': <function Employee.full_name at 0x7f859cef68c8>, 'apply_raise': <function Employee.apply_raise at 0x7f859cef6950>, '__dict__': <attribute '__dict__' of 'Employee' objects>, '__weakref__': <attribute '__weakref__' of 'Employee' objects>, '__doc__': None}
--------------------------
{'first': 'Harvey', 'last': 'Specter', 'pay': 1000000, 'email': 'Harvey.Specter@company.com'}

===== NAMESPACE AFTER MODIFICATION ========

{'__module__': '__main__', 'raise_amount': 1.04, '__init__': <function Employee.__init__ at 0x7f859cef6620>, 'full_name': <function Employee.full_name at 0x7f859cef68c8>, 'apply_raise': <function Employee.apply_raise at 0x7f859cef6950>, '__dict__': <attribute '__dict__' of 'Employee' objects>, '__weakref__': <attribute '__weakref__' of 'Employee' objects>, '__doc__': None}
--------------------------
{'first': 'Harvey', 'last': 'Specter', 'pay': 1000000, 'email': 'Harvey.Specter@company.com', 'raise_amount': 2}

Before Modification, the raise_amount only exists in the class Employee namespace.

After modification, the raise_amount also exists in object namespace.

So We can use this behaviour in custom situations according to the need, for example if we want in a company to give standard raise to all the employees but more than or less than standard raise to a specific employee than we can assign that raise_amount variable for that object and change the raise value for that specific object

If we want to count the number of employees or number of objects for any class than we can take a class variable and increment that variable in init method(constructor) so we can keep count of number of objects

PRO TIP : ONLY ACCESS CLASS VARIABLES USING CLASS NAME UNLESS YOU HAVE A SPECIAL USE CASE