Python – Object Oriented Programming

Python – Object Oriented Programming

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  Python – ObjectOriented Programming by Raghunath Akula
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  Classes & Objects Class serves as the primary means of abstraction in Object-Oriented programing.  A class provides a set of behaviors in the form of member_functions / methods, with implementation that are common to all instance.  In class, the state information for each instance is represented in the form of Attributes / Data members.  Instances are objects that are created which follow the definition given inside of the class.  No separate class interface definition. class MyVector: def __init__(self, x, y): self . x = x self . y = y def __add__(self, param2): return MyVector(self.x + param2.x, self.y + param2.y) Obj1 = MyVector(1, 2) “Object initiation for MyVector class.”
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  Access Specifiers  Pythonprovides a number of access modifiers to help you set the level of access for attributes and methods.  Private - 2 leading under-scores in its name, but none at the end. Can’t be accessed outside of class  Built-in – Methods or attributes having 2 underscores at the beginning and the end.  Doesn’t support ‘protected’. Subclasses would be unable to access these private data either. Garbage Collector  Python has automatic garbage collection.  Will automatically detect when all of the references to a piece of memory have gone out of scope. Automatically frees that memory.  There’s also no Destructor method for classes
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  Methods  Define amethod in a class by including function definitions within the scope of the class block  There must be a special first argument self in all of method definitions which gets bound to the calling instance  There is usually a special method called __init__ in most classes class MyVector: count = 0 “Class attribute” def __init__(self, x, y): self . x = x self . y = y def __add__(self, param2): return MyVector(self.x + param2.x, self.y + param2.y) def displayCount(self): count = self.x + self.y return count Obj1 = MyVector(1, 2) “Object initiation for MyVector class.” print Obj1.displayCount() “Calling displayCount method.”
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  Constructor ( __init__)  Serves as a constructor for a class.  The arguments passed to the class are given to its __init__() method def __init__(self, x, y): self . x = x self . y = y self  The first argument of every method is a reference to the current instance of the class  Parameter object self refers to current object being created, similar to keyword this in Java  Although self explicitly mentioned when defining the method, not mandatory included while calling the method. Self parameter is passed automatically by python.
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  Attributes Two Kinds ofAttributes: (1)Data Attributes Owned by particular instance of a class. Each instance has its own value for it. (2)Class Attributes All instance inside class share the same value for it. Similar to static variables or class-wide constants. “Example: Data Attributes” class MyVector: def __init__(self, x, y): self . x = x self . y = y “Example: Class Attributes” class MyVector: count = 0 “static variable” def displayCount(self): count = self.x + self.y return count
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  Inheritance  A classcan extend the definition of another class  Allows to use methods and attributes already defined in the previous classes.  To define a subclass, put the name of the superclass in parentheses “(…)”.  Python has no ‘extends’ keyword like Java. Python supports multiple inheritance. “Extending MyVector class” class SubVector (MyVector): def __init__(self, sub_x, sub_y): self . x = sub_x self . y = sub_y def displayCount(self): count = self.x + self.y return count
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  Method Overriding  Overridingis a very important part of OOP. It has the ability of a class to change the implementation of a method provided by one of its ancestors.  Python inheritance works through implicit delegation – when the object cannot satisfy a request, it forward request to its ancestors. “Parent Class” class MyVector: def __init__(self, x, y): self . x = x self . y = y def displayCount(self): return self.x + self.y “Child Class” class SubVector (MyVector): def displayCount(self): “Overriding dispalyCount method” return self.x + 10
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  Thank you!!