Three Elegant Python Tricks to Sum Columns in a 2D List

1. Introduction

A fan named dcpeng asked in a Python community how to sum the columns of a two‑dimensional list, as shown in the figure below.

The initial code works but requires a separate accumulator variable for each column, which becomes unwieldy when the sublists contain many elements.

2. Implementation

Solution by Yuliang

Yuliang provided a compact solution using list unpacking:

lst = [[1, 2, 3, 4], [1, 5, 1, 2], [2, 3, 4, 5], [5, 3, 1, 3]]
[print(sum(i)) for i in zip(*lst)]

Solution by Daler

Building on an earlier suggestion to use NumPy, Daler wrote:

import numpy as np

lst = [[1, 2, 3, 4], [1, 5, 1, 2], [2, 3, 4, 5], [5, 3, 1, 3]]
list1 = np.sum(lst, axis=0)  # column‑wise sum
list2 = np.sum(lst, axis=1)  # row‑wise sum
print(list1)
print(list2)

Solution by Moon God

Moon God offered a more advanced functional solution using built‑in functions and a lambda expression:

from functools import reduce

lst = [[1, 2, 3, 4],
       [1, 5, 1, 2, 6],
       [2, 3, 4, 5],
       [5, 3, 1, 3]]
print(list(reduce(lambda x, y: map(lambda i, j: i + j, x, y), lst)))

3. Summary

The three approaches demonstrate how to efficiently sum corresponding elements of each sublist in a regular 2D list using pure Python, NumPy, and functional programming techniques, providing clear code examples that help Python learners solve this common data‑processing task.