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Python Programming – Class Example
Class example
Till now, some basic concepts of class has been discussed. The following example “ClassExample.py” defines’a class Person, which handles name and age of multiple individuals.
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class Person:
" " "The program handles individual's data" " "
population=0
def ___init____ ( self , Name , Age ) :
" " "Initializes the data." " "
self.name=Name
self.age=Age
Person.population+=1
def ___del___ ( self ) :
" " "Deleting the data." " "
print ( ' Record of {0} is being removed'.format(self.name)) Person.population-=1
def AgeDetails ( self ) :
' ' 'Age details : ' ' '
print ( ' { 0 } is { 1 } years old ' . format ( self . name , self . age ) )
def Records ( cls) :
" " "Print number of records." " "
print ( ' There are {0} records ' . format ( cls.population ) )
records=classmethod ( Records )
print Person . ___doc___
record1=Person ( ' Ram ' , 26 )
print Person.AgeDetails. ___doc___
record1 . AgeDetails ( )
Person.records ( )
record2-Person ( ' Ahmed ' , 20 )
print record2 . AgeDetails. ___doc___
record2 . AgeDetails ( )
record2 . records ( )
record3=Person ( ' John ' , 22 )
print Person . AgeDetails. ___doc___
record3 . AgeDetails ( )
Person . records ( )
del recordl,record2
Person . records ( )
The output is:
The program handles individual's data Age details : Ram is 26 years old There are 1 records Age details : Ahmed is 20 years old There are 2 records Age details : John ih 22 years old There are 3 records Record of Ram is being removed Record of Ahmed is being removed There are 1 records
Variables defined in the class definition are class variables (population is a class variable); they are shared by all instances. To create instance variables (name and age are instance variables), they can be initialized in a method, e.g. self. name=value. Both class and instance variables are accessible through the notation self. name and an instance variable hide a class variable with the same name when accessed in this way. Therefore, the class variable population is better referred to as Person. population, and not-self. population. The instance variables name and age are referred to as self. name and self. age, respectively.
The Records is a method that belongs to the class and not to the instance. This is done by using classmethod ( ) built-in function. A class method receives the class as an implicit first argument, just like an instance method receives the instance. The class method can be called either on the class (Person. records ( )) or on an instance (record2 . records ( )). The instance is ignored except for its class.
The ___doc___ attribute is used to access docstrings of class (Person. ___doc___ ) and methods (record2 . AgeDetails . __doc___).
The ___del___ ( ) method is called when an instance is about to be destroyed. This is also called a destructor.
