The reduce() function in Python is a function that implements a mathematical technique called ‘folding’ or 'reduction'. In this tutorial, we'll figure out why we get "NameError: the name 'reduce' is not defined", and learn how to fix it.

What is “reduce is not defined” in Python?

In Python “reduce is not defined” is a NameError that we get when we try to use the reduce() function without importing it.

Why do we get “reduce is not defined” error?

We get a "NameError: name 'reduce' is not defined" when trying to use the reduce() function because the reduce function has been removed from Python3 built-in functions and moved to the “functools” module.

How to fix "NameError: name 'reduce' is not defined"?

There are two simple ways of fixing this error:

Solution 1: import “functools” module

without importing reduce() from 'functools'

def do_math(x, y):
&nbsp&nbspreturn x + y

print(reduce(do_math, [5, 5, 3], 7))

after importing reduce() from 'functools'

from functools import reduce

def do_math(x, y):
&nbsp&nbspreturn x + y

print("After importing we get -",reduce(do_math, [5, 5, 3], 7))

Output:

name-error-functools after-importing-functools

Solution 2: use the “six” library

importing reduce from "six" libraries

def do_math(x, y):
&nbsp&nbspreturn x + y

print(reduce(do_math, [5, 5, 3], 7))


# importing reduce from "six" libraries
from six.moves import reduce

def do_math(x, y):
&nbsp&nbspreturn x + y

print("Using six library we get -",reduce(do_math, [5, 5, 3], 7))

Output:

name-error-functools after-six-library

Conclusion In this tutorial, we figured out where the "NameError: name 'reduce' is not defined" is coming from and covered two ways to fix this error.