Python session 7 by Shan


A user-defined prototype for an object that defines a
set of attributes that characterize any object of the
class. The attributes are data members (class variables
and instance variables) and methods, accessed via dot
notation.
Class


A variable that is shared by all instances of a class.
Class variables are defined within a class but outside
any of the class's methods.

Class variables aren't used as frequently as instance
variables are.
Class variable


The class statement creates a new class definition.

The name of the class immediately follows the
keyword class followed by a colon as follows:

Class ClassName:

‘Optional class documentation string‘

class_suite
Creating Classes


The class has a documentation string, which can be
accessed via ClassName.__doc__.

The class_suite consists of all the component
statements defining class members, data attributes and
functions.

Class Employee:
'Common base class for all employees'
empCount = 0
def __init__(self, name, salary):
self.name = name
self.salary = salary
Employee.empCount += 1


The first method __init__() is a special method, which
is called class constructor or initialization method that
Python calls when you create a new instance of this
class.

def displayCount(self):

print "Total Employee %d" Employee.empCount

def displayEmployee(self):

print "Name : ", self.name, ", Salary: ", self.salary

"This would create first object of Employee class"
emp1 = Employee("Zara", 2000)
"This would create second object of Employee class"
emp2 = Employee("Manni", 5000)
emp1.displayEmployee()
emp2.displayEmployee()
print "Total Employee %d" % Employee.empCount

Name : Zara ,Salary: 2000
Name : Manni ,Salary: 5000
Total Employee 2
Output


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 you 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.
Class Inheritance

class Parent: # define parent class
parentAttr = 100
def __init__(self):
print "Calling parent constructor"
def parentMethod(self):
print 'Calling parent method'
def setAttr(self, attr):
Parent.parentAttr = attr

def getAttr(self):
print "Parent attribute :", Parent.parentAttr
class Child(Parent): # define child class
def __init__(self):
print "Calling child constructor"
def childMethod(self):
print 'Calling child method'
c = Child() # instance of child

c.childMethod() # child calls its method
c.parentMethod() # calls parent's method
c.setAttr(200) # again call parent's method
c.GetAttr() # again call parent's method

Output:
Calling child constructor
Calling child method
Calling parent method
Parent attribute : 200

Python session 7 by Shan

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Python session 7 by Shan