Multimethods in Python

Multimethod basically means a function that has multiple versions, distinguished by the type of the arguments. For better understanding consider the below example.

@multimethod
def sum(x: int, y: int):
    return x + y

@multimethod
def sum(x: str, y: str):
    return x+" "+y

The above example is similar to

def sum(x, y):
    
    if isinstance(x, int) and isinstance(y, int):
        return x + y
    
    elif isinstance(x, str) and isinstance(y, str):
        return x + ' ' + y

Installation

At syntactical level, Python does not support multiple dispatch but it is possible to add multiple dispatch using a library extension multimethod. To install this library type the below command in the terminal.

pip install multimethod

Example 1:

# Python program to demonstrate
# multimethods


from multimethod import multimethod


# Function that will be called
# for integer addition
@multimethod
def sum(x: int, y: int):
    return x + y

# Function that will be called
# for string addition
@multimethod
def sum(x: str, y: str):
    return x+" "+y

# Driver's code
print(sum(2, 3))
print(sum("Hello", "World"))

Output:

5
Hello World

Example 2:

# Python program to demonstrate
# multimethods


from multimethod import multimethod


class GFG(object):

    @multimethod
    def double(self, x: int):
        print(2 * x)

    @multimethod
    def double(self, x: complex):
        print("sorry, I don't like complex numbers")

# Driver Code
obj = GFG()
obj.double(3)
obj.double(6j)

Output:

6
sorry, I don't like complex numbers