Method overloading

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Several ways to call a method (method overloading)

In Python you can define a method in such a way that there are multiple ways to call it.

Given a single method or function, we can specify the number of parameters ourself.

Depending on the function definition, it can be called with zero, one, two or more parameters.

This is known as method overloading. Not all programming languages support method overloading, but Python does.

Method overloading example

We create a class with one method sayHello(). The first parameter of this method is set to None, this gives us the option to call it with or without a parameter.

An object is created based on the class, and we call its method using zero and one parameter.

#!/usr/bin/env python

class Human:

    def sayHello(self, name=None):
    
        if name is not None:
            print('Hello ' + name)
        else:
            print('Hello ')
        

# Create instance
obj = Human()
    
# Call the method
obj.sayHello()
    
# Call the method with a parameter
obj.sayHello('Guido')

Output:

Hello
Hello Guido

To clarify method overloading, we can now call the method sayHello() in two ways:

obj.sayHello()
obj.sayHello('Guido')

We created a method that can be called with fewer arguments than it is defined to allow.

We are not limited to two variables, your method could have more variables which are optional.

If you are new to Python programming, I highly recommend this book.

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Posted in beginner

2016-03-09

Leave a Reply:

Christian Ransom • Fri, 24 Jul 2015

So to clarify, if no argument is given for the second parameter, the second parameter will be set to None?

Frank • Fri, 24 Jul 2015

Yes, if no parameter is given it will be set to None. There is no limit to the number of parameters you pass.
You could have a method that accepts multiple parameters:

#!/usr/bin/env python
 
class Human:
 
    def sayHello(self, name=None, age=None):
 
        if name is not None:
            print 'Hello ' + name
        else:
            print 'Hello '

        if age is not None:
            print 'Age = ' + str(age)

# Create instance
obj = Human()
 
# Call the method
obj.sayHello()
 
# Call the method with a parameter
obj.sayHello('Guido')

# Call with two parameters
obj.sayHello('Guido',18)

Andrew • Sat, 25 Jul 2015

What abou situation: we have no first argument, and have the second?

Frank • Sat, 25 Jul 2015

Hi Andrew, you could pass the first parameter as None. An alternative would be to pass an instance of a class (an object) to a method, which is what I recommend if you want to pass a lot of variables.

Kurtis • Wed, 09 Sep 2015

Can you have other variables in overloading besides none? Such as def sayHello(self, name='Default User'): ?

Frank • Wed, 09 Sep 2015

This seems to work. Usually constant variables are defined in the local scope of the function, you could use it as default value for a parameter.

Andrew • Wed, 09 Sep 2015

Thank you. It looks easier)

Add • Thu, 26 Nov 2015

Hello, how can i do that?(last command)

#!/usr/bin/env python
 
class Human:
 
    def sayHello(self, name=None, age=None):
 
        if name is not None and age is None:
            print ('Hello ' + name)


        elif age is not None and age is not None:
            print ('Hello ' + name + ' your are ' + age + ' years old !')
        else:
            print ('Hello ')
 
# Create instance
obj = Human()
 
# Call the method
obj.sayHello()
 
# Call the method with a parameter
obj.sayHello( 'Ad', '23')

obj.sayHello(, '23')

Frank • Sun, 29 Nov 2015

Try None for the first argument.

Harsh • Mon, 21 Dec 2015

it didn't work for me by writing none for the first arguement !!

Frank • Sat, 26 Dec 2015

Change the function to:

    def sayHello(self, name=None, age=None):
        if name is not None and age is None:
            print ('Hello ' + name)
        elif name is not None and age is not None:
            print ('Hello ' + name + ' your are ' + str(age) + ' years old !')
        else:
            print ('Hello ')

Sadia • Mon, 11 Jan 2016

Dear Frank,
i want some help in packages. i have not found any article related to packages on this website. sorry i am posting my question in this method overloading section. I have made three packages named Data, Student and postgraduate. postgraduate is subpackage of student package. there are files : biodata.py and _init_.py in student and subjects.py and_init_.py in postgraduate respectively.
code in biodata.py:

class Student_Info:

    def personal_info(self,name,age,roll_no):
        print("age is",self.name)
        print("name is",self.age)
        print("roll no is",self.roll_no)

code in subject.py

class Info:

    def display(self):
        print("the subjects are")
        print("OOP")
        print("DBMS")

in package Data there are two files _init_.py and test.py
i want to access the methods of student_info and info into Data package. i mean by running Data package i could see output of these methods here. for this purpose i have written this code in test.py

import student.postgraduate
import student

class Data_display:

    def method(self):
        print("this will display data")


obj=Student_Info()
obj.personal_info("sadia",12,"Reg_09")
obj2=Info()
obj2.display()

i am getting error on object creation. (obj=Student_Info() and obj2=Info() . please tell me what i am doing wrong in this program.
thank you

Frank • Sat, 30 Jan 2016

Hi Sadia,you are missing some imports:

from biodata import Student_Info
from subject import Info

Presently an object of student_info is not given a name or age. We can set the object variables by using a constructor.
I've changed biodata.py (Student_Info) class:

class Student_Info:

    name = ""
    age = 0
    roll_no = 0

    def __init__(self,name,age,roll_no):
        self.name = name
        self.age = age
        self.roll_no = roll_no

    def personal_info(self):
        print("age is",self.name)
        print("name is",self.age)
        print("roll no is",self.roll_no)

Changed test.py to

from biodata import Student_Info
from subject import Info

class Data_display:

    def method(self):
        print("this will display data")


obj=Student_Info("sadia",12,"Reg_09")
obj.personal_info()

obj2=Info()
obj2.display()

Jatin Vamja • Tue, 02 Feb 2016

try last function as following
obj.sayhello(age=23)

Jatin Vamja • Tue, 02 Feb 2016

__author__ = 'jatin'
try this i m getting output

class Human:
    def sayHello(self, name=None, age=None):
        if name is not None and age is None:
            print ('Hello ' + name)
        elif age is not None and name is not None:
            print ('Hello ' + ' your are ' + age + ' years old !')
        else:
            print ('Hello ')

# Create instance
obj = Human()
# Call the method
obj.sayHello()
# Call the method with a parameter
obj.sayHello( 'Ad', '23')
obj.sayHello(age=23)

Radek Duda • Fri, 09 Jun 2017

Just short notice about boolean condition. It could be shortened from the form:


if name is not None:


if name: