Python - Method Overloading

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Method overloading is an important feature of object-oriented programming. Java, C++, C# languages support method overloading, but in Python it is not possible to perform method overloading.

When you have a class with method of one name defined more than one but with different argument types and/or return type, it is a case of method overloading. Python doesn't support this mechanism as the following code shows −

Example

class example:
   def add(self, a, b):
      x = a+b
      return x
   def add(self, a, b, c):
      x = a+b+c
      return x

obj = example()

print (obj.add(10,20,30))
print (obj.add(10,20))

Output

The first call to add() method with three arguments is successful. However, calling add() method with two arguments as defined in the class fails.

60
Traceback (most recent call last):
 File "C:\Users\user\example.py", line 12, in <module>
  print (obj.add(10,20))
         ^^^^^^^^^^^^^^
TypeError: example.add() missing 1 required positional argument: 'c'

The output tells you that Python considers only the latest definition of add() method, discarding the earlier definitions.

To simulate method overloading, we can use a workaround by defining default value to method arguments as None, so that it can be used with one, two or three arguments.

Example

class example:
   def add(self, a = None, b = None, c = None):
      x=0
      if a !=None and b != None and c != None:
         x = a+b+c
      elif a !=None and b != None and c == None:
         x = a+b
      return x

obj = example()

print (obj.add(10,20,30))
print (obj.add(10,20))

It will produce the following output −

60
30

With this workaround, we are able to incorporate method overloading in Python class.

Python's standard library doesn't have any other provision for implementing method overloading. However, we can use dispatch function from a third party module named MultipleDispatch for this purpose.

First, you need to install the Multipledispatch module.

pip install multipledispatch

This module has a @dispatch decorator. It takes the number of arguments to be passed to the method to be overloaded. Define multiple copies of add() method with @dispatch decorator as below −

Example

from multipledispatch import dispatch
class example:
   @dispatch(int, int)
   def add(self, a, b):
      x = a+b
      return x
   @dispatch(int, int, int)
   def add(self, a, b, c):
      x = a+b+c
      return x

obj = example()

print (obj.add(10,20,30))
print (obj.add(10,20))

Output

60
30