3.3. Functools

functools is a built-in Python library to work with functions efficiently. This section will show you some useful methods of functools.

3.3.1. functools.partial: Generate a New Function with Fewer Arguments

If you want to fix some arguments of a function and generate a new function with fewer arguments, use functools.partial.

In the code below, I use partial to create a new function with only x as the argument.

from functools import partial

def linear_func(x, a, b):
    return a * x + b

linear_func_partial = partial(linear_func, a=2, b=3)

3.3.2. functools.singledispatch: Call Another Function Based on the Type of the Current Function’s Argument

Normally, to call another function based on the type of the current function’s argument, we use an if-else statement:

data = {"a": [1, 2, 3], "b": [4, 5, 6]}
data2 = [{"a": [1, 2, 3]}, {"b": [4, 5, 6]}]
def process_data(data):
    if isinstance(data, dict):


def process_dict(data: dict):
    print("Dict is processed")

def process_list(data: list):
    print("List is processed")
Dict is processed
List is processed

With singledispatch, you don’t need to use an if-else statement to call an appropriate function. singledispatch will choose the right function based on the type of current function’s first argument.

from functools import singledispatch

def process_data2(data):
    raise NotImplementedError("Please implement process_data2")

def process_dict2(data: dict):
    print("Dict is processed")

def process_list2(data: list):
    print("List is processed")
Dict is processed
List is processed