Vectors the Pythonic Way

Photo by George Pagan III on Unsplash

There are many ways to achieve the same task in python, but there is a preferred way. For your code to be pythonic, it should comply with the zen of python (PEP20).

import this

Setup:

Let us have a look at three different ways to sum vectors (a vector is a list of floats):

vectors = [[1.5, 2.5, 3.5],
           [3.5, 4.5, 5.5],
           [5.5, 6.5, 7.5],
           [7.5, 8.5, 9.5]]

Note: vectors are of equal length.

The pythonic way:

[sum(vector[i]
        for vector in vectors)
        for i in range(len(vectors[0]))]    # -> [18.0, 22.0, 26.0]

This way utilizes comprehension lists. It’s explicit and readable.

The non-pythonic way:

res = []
for i in range(len(vectors[0]):
    temp = 0
    for vector in vectors:
        temp += vector[i]
    res.append(temp)
res    # -> [18.0, 22.0, 26.0]

This way is explicit because it uses for loops. But when it comes to python, there should be one and only one preferable way.

The functional way:

from functools import reduce
list(map(sum, zip(*vectors)))    # -> [18.0, 22.0, 26.0]

This way is implicit since a functional line of codes tends to be declarative.

I hope this gave you a broad perspective of different ways to achieve the same task. Moreover, the pythonic way is not black or white; for example, the non-pythonic way is pythonic to an extent, but since there is a better way (comprehension lists), it took second place.