Learning Python: Programming and Data Structures- Tutorial 9- Operator Overloading


Operator Overloading mean, that we re-define certain common operators and methods, to work in a customized manner.

Say, we have a class which holds academic records for Students. And, when we say that student1 < student2;  we mean to say that the aggregate scores of Student2 are higher than the same for Student1.
For this, we will override the __lt__ (less than) function, in class Student to behave in this customized manner.Similarly, we can redefine the addition operator (+), multiplication, subtraction, power operators by redefining the __add__, __mult__, __sub__, __pow__ functions.
Take a look at the special method names over here:  Special method names. This will give you an idea of method names which can be overridden.
Let us take a quick look at this simple example for students, described above. We are going to overload the > operator (greater than) in this example.


# Let's define a class student, with the name of the student, and the student's score in Math and English
class student:

	def __init__(self,name,percentageScoreInMathematics,percentageScoreInEnglish):
		self.name = name
		self.percentageScoreInMathematics = percentageScoreInMathematics
		self.percentageScoreInEnglish = percentageScoreInEnglish


	# This is where we will try out overloading
	# We will overload the > symbol.
	# So, we include this __gt__ function (lt stands for less than)
	# Student1 is supposed to be 'greater than' student 2 if his aggregate score in Math and English is greater than that of Student2
	def __gt__(self,secondStudent):
		return (self.percentageScoreInMathematics + self.percentageScoreInEnglish) > (secondStudent.percentageScoreInMathematics + secondStudent.percentageScoreInEnglish)

	# A function to display the name and scores(in Math and English) of the student
	def displayDetails(self):
		print self.name + " Mathematics Score =" + `self.percentageScoreInMathematics` + " English Score =" + `self.percentageScoreInEnglish` + '\n'
		

	


# Let us create 2 objects corresponding to two students
firstStudent = student('Ankit',98,99)
secondStudent = student('Jack',90,95)


# Let us display the details of these two students
firstStudent.displayDetails()
secondStudent.displayDetails()


# Now let us use the overloaded > operator to compare the two students and find out who is the better one in terms of aggregate scores
print "Records of the better student:"
print "We will use the overridden > operator to do this"
# Now we will compare the two students with the overloaded 'greater than' > sign
if firstStudent > secondStudent:
	firstStudent.displayDetails()
else:
	secondStudent.displayDetails()
 

Output from the above program:

~/work/pythontutorials$ python operatorOverloading.py 
Ankit Mathematics Score =98 English Score =99

Jack Mathematics Score =90 English Score =95

Records of the better student:
We will use the overridden > operator to do this
Ankit Mathematics Score =98 English Score =99