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Python reduce explained

Welcome to the next pikoTutorial!

The reduce function is a powerful tool placed in the functools module that facilitates the cumulative application of a function to the items of an iterable (from left to right), to reduce them to a single value. Initially introduced in Python 2, later moved to functools in Python 3, reduce is similar to the concept of folding in functional programming languages.

Syntax and parameters

The syntax of the reduce function is:

Python
reduce(function, iterable[, initializer])
  • function: this is a function that takes two arguments and returns a single value. It is applied cumulatively to the items of iterable.
  • iterable: this is a sequence of elements like a list, tuple, etc. that reduce operates on sequentially.
  • initializer (optional): this is an initial value that serves as the starting point for the cumulative computation. If provided, reduce starts with this value and the first item of the iterable.

How to use it

Let’s illustrate it with a simple example to find the product of elements in a list:

Python
from functools import reduce

numbers = [1, 2, 3, 4, 5]
product = reduce(lambda x, y: x * y, numbers)
print(product)

This code generates the result of multiplication 1 * 2 * 3 * 4 * 5 which is 120. If you add an initializer, for example value 10:

Python
product = reduce(lambda x, y: x * y, numbers, 10)

The result will be equal to 1200 because now it starts with the value 10: 10 * 1 * 2 * 3 * 4 * 5.

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