I recently learned the object oriented part of Python. The concepts are similar to any other object oriented programming language.

Creating a class with constructor-

class Employee:
    def __init__(self, first, last):
        self.first = first
        self.last = last        
    def fullname(self)
        return self.first + " " + self.last
emp1 = Employee('Nikhil', 'Gupta')
print(emp1.fullname())
#print(Employee.fullname(emp1))

Points to note-

1. __init__ function acts as a constructor.
2. The first parameter is the object reference which is passed automatically to all the functions of the class. It is named as self by convention.
3. emp1.fullname() and Employee.fullname(emp1) are equivalent. When object name is used, the reference is passed automatically. When the class name is used, object reference (that is self) needs to be passed explicitly.

Class Variables

These variables are common for all objects of that class.

class Employee:
    raise_amt = 1.05
    def __init__(self, first, last, pay):
        self.first = first
        self.last = last
        self.pay = pay
    def apply_raise(self):
        self.pay = int(self.pay * Employee.raise_amt)

##########################################

emp1 = Employee('Nikhil', 'Gupta', 5000)
emp2 = Employee('Niki', 'Gupta', 10000)

print(emp1.raise_amt) # prints 1.05
print(emp2.raise_amt) # prints 1.05
print(Employee.raise_amt) # prints 1.05

emp1.apply_raise()
print(emp1.pay) # prints 5250

##########################################

Employee.raise_amt = 1.1

print(emp1.raise_amt) # prints 1.1
print(emp2.raise_amt) # prints 1.1
print(Employee.raise_amt) # prints 1.1

print(emp1.__dict__) # prints {'pay': 5250, 'first': 'Nikhil', 'last': 'Gupta'}
print(emp2.__dict__) # prints {'pay': 10000, 'first': 'Niki', 'last': 'Gupta'}
print(Employee.__dict__) # prints {...,'raise_amt': 1.1,...}

##########################################

emp2.raise_amt = 1.05

print(emp1.raise_amt) # prints 1.1
print(emp2.raise_amt) # prints 1.05
print(Employee.raise_amt) # prints 1.1

print(emp1.__dict__) # prints {'pay': 5250, 'first': 'Nikhil', 'last': 'Gupta'}
print(emp2.__dict__) # prints {'first': 'Niki', 'last': 'Gupta', 'raise_amt': 1.05, 'pay': 10000}
print(Employee.__dict__) # prints {...,'raise_amt': 1.1,...}

Points to note-

1. Object namespace is searched first, for the variable. If it isn’t found there, class namespace is searched.
2. This allows setting a common class variable for all objects and if need be, that variable can be tinkered for individual objects.