Python Note 6(Classes and Objects)

Sample Code  : General class

#define a class
class User :
 def __init__(self,name,user_id,acc_balance):
  self.Name=name
  self.User_id=user_id
  self.Acc_Balance=acc_balance
  
 def recharge(self,amount):
  self.Acc_Balance+=amount
 
 def withdraw(self,amount):
  if amount <= self.Acc_Balance :
   self.Acc_Balance-=amount
  else :
   pass #do nothing
 
 def getBalance(self): #parameter less method
  return self.Acc_Balance
  
 def __del__(self) :
  print("Destructor started!")
#end of the class
 
usr=User("Kanishka",1133,27000.00)
print("User {0} , Balance {1:5.2f}".format(usr.Name,usr.getBalance()))
usr.withdraw(2000.50) #withdrwaw money
print("User {0} , Balance {1:5.2f}".format(usr.Name,usr.getBalance()))

• Encapsulation 

Python has mainly 3 access modifiers

• public 
• protected : Variable name started with single _ character (ex: _userName )
• private : Variable name started with tow _ character (ex: __userName )

Lets rewrite above class with encapsulation

#define a class
class User :
 def __init__(self,name,user_id,acc_balance):
  self.__Name=name  #private
  self.__User_id=user_id  #private
  self.__Acc_Balance=acc_balance #private
  
 def recharge(self,amount):
  self.Acc_Balance+=amount
 
 def withdraw(self,amount):
  if amount <= self.__Acc_Balance :
   self.__Acc_Balance-=amount
  else :
   pass #do nothing
 
 def getBalance(self): #parameter less method
  return self.__Acc_Balance
  
 def getUserName(self) :
  return self.__Name
  
 def __del__(self) :
  print("Destructor started!")
 
#end of the class
 
usr=User("Kanishka",1133,27000.00)
print("User {0} , Balance {1:5.2f}".format(usr.getUserName(),usr.getBalance()))
usr.withdraw(2000.50) #withdrwaw money
print("User {0} , Balance {1:5.2f}".format(usr.getUserName(),usr.getBalance()))

• Inheritane

Note : Python supports multiple inheritance
Code :

class Person :
 def __init__(self,nic,name,address) :
  self._name=name #protected
  self._nic=nic
  self._address=address
 
 def __del__(self) :
  print("Destructor started!")
#class ended
 
class Employee(Person) : #inherit the person class
 def __init__(self,nic,name,address,employeeID,salary):
  Person.__init__(self,nic,name,address)
  self._employeeID=employeeID
  self._salary=salary
 
 def __del__(self) :
  print("Destructor started!")
#class ended

p=Person("832355234V","Saman","Sri Lanka")
print ("Person instance")
print ("Name : {} ".format(p._name))

e=Employee("881302333V","Kanishka","Sri Lanka",2328,20000)
print ("Employee instance")
print ("Name : {} ".format(e._name))
print ("employeeID : {0:d} ".format(e._employeeID))