object oriented

1. procedure-oriented: we design program around function,blocks of statements which manipulate data.
   object-oriented:We organize program which is to combine data and functionality and wrap it inside something called an object
2. Two main aspect: classes and objects
   A class creats a new type where objects are instances of the class
3. fields:Variable that belong to an object or class are referred to as fields
   method:Objects can have functionality by using functions that belong to a class.Such functions are called methods of the class
4. Fileds are of two types-They can belong to each instance/object of the class or they can belong to the class itself.They are called instance variable or class variable
5. A class is created using the class keyword.The fields and methods of the class are listed in an indented block.
6. Class method have only one specific difference from ordinary function-they must have an extra first name that has to be added to the beginning of the parameter list,but you don’t give a value for this parameter when you call the method,Python will provide it.This particular variable refers to the object itself,and by convention,it is given the name ‘self’
7. Example:
   

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   class Person: def say_hi(self): print('Hello World') p=Person() p.say_hi()

• Notice that the say_hi()method takes no parameters but still has the self in the function definition

1. init method:This method is run as soon as an object of a class is created,which is useful to do any initialization.

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   class Person: def __init__(self,name): self.name=name def say_hi(self): print('Hello,',self.name) p=Person('Tom') p.say_hi()

2. Class and Object Variation

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   class Robot: """Represent a robot,with a name.""" #A class varible,counting the number of robots population=0 def __init__(self,name): """Initializes the data.""" self.name=name print("(Initializing {}).".format(self.name)) #When this person is created,the robot adds to the population Robot.population+=1 def die(self): """I'm dying""" print("{} is being destroyed!".format(self.name)) Robot.population-=1 if Robot.population==0: print("{} was the last one.".format(self.name)) else: print('There are still {:d} robots working'.format(Robot.population)) def say_hi(self): """greeting by robot. Yeah,they can do that.""" print("Greeting,my masters call me {}.".format(self.name)) @classmethod def how_many(cls): """print the current population.""" print('We have {:d} robots'.format(cls.population)) droid1=Robot('R2-D2') droid1.say_hi() droid1.how_many()#???? Robot.how_many()#droid1 and Robot both? droid2=Robot('R3-D3') droid2.say_hi() Robot.how_many() droid1.die() droid2.die() Robot.how_many()

output:

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[email protected]:~/Python$ python3 heritance.py 
Initialized schoolMember:Tom
(Initialized Teacher:Tom)
Initialized schoolMember:Jim
(Initialized Student:Jim)

Name:"Tom" Age:"40"Salary:"30000"
Name:"Jim" Age:"10"Marks:"80"

• Since we are defining a init method in Teacher and Student subclasses,Python does not automatically call the constructor of the base class schoolMember,you have to explicitly call it yourself.In contrast,if we have not defined an init method in a subclass.Python will call the constructor of the base class automatically.
• Python always starts looking at the method in the actual subclass type first,and if it doesn’t find anything,it starts looking at the method in subclass’s base classes,one by one in the order.