Teaching Kids Programming – Compute the Dot Product using Zip Function in Python

Teaching Kids Programming: Videos on Data Structures and Algorithms

Given two vectors of same length, a and b represented by two lists/array in Python, the dot product is defined as follows:

where n is the length of both vectors.

Compute the Dot Product in Python

Traditional loop – going through each index:

def dot(a, b):
    n = len(a)
    assert n == len(b)
    s = 0
    for i in range(a):
        s += a[i] * b[i]
    return s

Example: dot([1,2,3],[4,5,6]) = 1*4+2*5+3*6=32

We can implement this using one-liner in Python with help of the zip function:

def dot(a, b):
    n = len(a)
    assert n == len(b)
    return sum(x[0] * x[1] for x in zip(a, b))

The time complexity of dot product computation is O(N) – as we need to go through two arrays in pairs. The space complexity is O(1) constant.

The assert function makes sure the lengths are equal for both vectors – it will stop executing the rest of the code once the condition is not met (check fails)

   
Traceback (most recent call last):
  File "main.py", line 9, in <module>
    print(dot([1, 2, 3, 4], [4, 5, 6]))
  File "main.py", line 6, in dot
    assert n == len(b)
AssertionError
</module>

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