reduce() in Python

Last Updated : 9 Jun, 2026

reduce() function (from the functools module) applies a function cumulatively to the elements of an iterable and returns a single final value. It processes elements step-by-step, combining two elements at a time until only one result remains.

Example: In this example, reduce() combines all strings in a list into one sentence.

Explanation: reduce(lambda x, y: x + " " + y, a) joins elements step-by-step into one string.

Syntax

reduce(function, iterable[, initializer])

Parameters:

function: A function that takes two arguments and returns a single value.
iterable: The sequence to be reduced (list, tuple, etc.).
initializer (optional): A starting value that is placed before first element.

Returns: Returns a single final value after processing all elements.

Examples

Example 1: Here, the code adds all numbers in a list using reduce(). The function combines two numbers at a time.

Explanation: reduce(lambda x, y: x + y, a) adds elements step-by-step ((2 + 4) + 6) + 8 = 20.

Example 2: Here, the code finds the largest number from a list using reduce().

Explanation: lambda x, y: x if x > y else y compares two values at each step and keeps the larger one, resulting in the maximum value 12.

Example 3: This example uses functools.reduce() with built-in functions from operator module to perform sum, product and string concatenation on lists.

Output

17
180
geeksforgeeks

Explanation:

functools.reduce(operator.add, a) adds all numbers in the list 1+3+5+6+2 = 17.
functools.reduce(operator.mul, a) multiplies all numbers in the list 1*3*5*6*2 = 180.
functools.reduce(operator.add, ["geeks", "for", "geeks"]) concatenates all strings in list "geeksforgeeks"

Difference Between reduce() and accumulate()

accumulate() function (from itertools) and reduce() both apply a function cumulatively to items in a sequence. However, accumulate() returns an iterator of intermediate results, while reduce() returns only final value.

Example: This code demonstrates how accumulate() from itertools module works it performs cumulative operations and returns all intermediate results instead of just a single final value.

Explanation: accumulate(a, add) - Adds elements cumulatively:

Step 1: 1
Step 2: 1 + 2 = 3
Step 3: 3 + 3 = 6
Step 4: 6 + 4 = 10
Step 5: 10 + 5 = 15

Let's understand the difference between accumulate() and reduce() more clearly with the help of the table below:

Feature	reduce()	accumulate()
Return Value	A single final value (e.g., `15`).	Intermediate results (e.g., [1, 3, 6, 10, 15]).
Output Type	Returns a single value.	Returns an iterator.
Use Case	Useful when only the final result is needed.	Useful when tracking cumulative steps.
Import	From functools.	From itertools.

漫思

posted on 2026-06-10 20:02 漫思阅读(4) 评论() 收藏举报

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reduce() in Python

Syntax

Examples

Difference Between reduce() and accumulate()