Programming Articles - Page 3252 of 3363

Object-oriented programming creates reusable patterns of code to prevent code redundancy in projects. One way that recyclable code is created is through inheritance, when one subclass leverages code from another base class.Inheritance is when a class uses code written within another class.Classes called child classes or subclasses inherit methods and variables from parent classes or base classes.Because the Child subclass is inheriting from the Parent base class, the Child class can reuse the code of Parent, allowing the programmer to use fewer lines of code and decrease redundancy.Derived classes are declared much like their parent class; however, a list of ... Read More

The code below shows the if the attribute 'foo' was defined or derived in the classes A and B.Exampleclass A:     foo = 1 class B(A):     pass print A.__dict__ #We see that the attribute foo is there in __dict__ of class A. So foo is defined in class A. print hasattr(A, 'foo') #We see that class A has the attribute but it is defined. print B.__dict__ #We see that the attribute foo is not there in __dict__ of class B. So foo is not defined in class B print hasattr(B, 'foo') #We see that class B has ... Read More

We have the classes A and B defined as follows −class A(object): pass class B(A): passExampleA can be proved to be a super class of B in two ways as followsclass A(object):pass class B(A):pass print issubclass(B, A) # Here we use the issubclass() method to check if B is subclass of A print B.__bases__ # Here we check the base classes or super classes of BOutputThis gives the outputTrue (,)

We have the classes A and B defined as follows −class A(object): pass class B(A): passB can be proved to be a sub class of A in two ways as followsclass A(object):pass class B(A):pass print issubclass(B, A) # Here we use the issubclass() method to check if B is subclass of A print B.__bases__ # Here we check the base classes or super classes of BThis gives the outputTrue (,)

We can derive a class from multiple parent classes as follows −class A:        # define your class A ..... class B:         # define your class B ..... class C(A, B):   # subclass of A and B .....We can use isinstance() function to check the relationships of two classes and instances.Theisinstance(obj, Class) boolean function returns true if obj is an instance of class Class or is an instance of a subclass of Class

We can derive a class from multiple parent classes as follows −class A:        # define your class A ..... class B:         # define your class B ..... class C(A, B):   # subclass of A and B .....We can use issubclass() function to check the relationships of two classes and instances.For example, theissubclass(sub, sup) boolean function returns true if the given subclass sub is indeed a subclass of the superclass sup.

Inheritance in classesInstead of defining a class afresh, we can create a class by deriving it from a preexisting class by listing the parent class in parentheses after the new class name.The child class inherits the attributes of its parent class, and we can use those attributes as if they were defined in the child class. A child class can also override data members and methods from the parent.SyntaxDerived classes are declared much like their parent class; however, a list of base classes to inherit from is given after the class name −class SubClassName (ParentClass1[, ParentClass2, ...]):    'Optional class ... Read More

Python deletes unwanted objects (built-in types or class instances) automatically to free the memory space. The process by which Python periodically frees and reclaims blocks of memory that no longer are in use is called Garbage Collection.Python's garbage collector runs during program execution and is triggered when an object's reference count reaches zero. An object's reference count changes as the number of aliases that point to it changes.An object's reference count increases when it is assigned a new name or placed in a container (list, tuple, or dictionary). The object's reference count decreases when it's deleted with del, its reference is ... Read More

When an object is deleted or destroyed, a destructor is invoked. Before terminating an object, cleanup tasks like closing database connections or filehandles are completed using the destructor. The garbage collector in Python manages memory automatically. for instance, when an object is no longer relevant, it clears the memory. In Python, the destructor is entirely automatic and never called manually. In the following two scenarios, the destructor is called − When an object is no longer relevant or it goes out of scope The object's reference counter reaches zero. Using the __del__() method In Python, a destructor is ... Read More

A class attribute is an attribute of the class rather than an attribute of an instance of the class.In the code below class_var is a class attribute, and i_var is an instance attribute: All instances of the class have access to class_var, which can also be accessed as a property of the class itself −Exampleclass MyClass (object):     class_var = 2     def __init__(self, i_var):         self.i_var = i_var foo = MyClass(3) baz = MyClass(4) print (foo.class_var, foo.i_var) print (baz.class_var, baz.i_var)OutputThis gives the output(2, 3) (2, 4)