Easy

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zip: Walking Two Lists Together

~8 mincode completion

zip pairs up two (or more) collections and lets you loop over both at once:

names = ["ada", "grace"]
ages = [36, 45]

for name, age in zip(names, ages):
    print(name, age)
# ada 36
# grace 45

If the lists are different lengths, zip stops at the shorter one. That is occasionally what you want and is very often a silent bug, so check your lengths when it matters.

This pattern shows up everywhere in machine learning: predictions and true labels are two parallel lists, and almost every metric is a loop over their pairs.

Your task:

Write dot_product(a, b) that multiplies the two lists element by element and returns the total.

For [1, 2, 3] and [4, 5, 6] that is 1*4 + 2*5 + 3*6, which is 32.

You will meet this operation again as the core of every linear model.

Example Tests

The worked example from the prompt

Input: {"a":[1,2,3],"b":[4,5,6]}

Expected: 32

Multiplying by zeros contributes nothing

Input: {"a":[1,2],"b":[0,0]}

Expected: 0

Negative values subtract from the total

Input: {"a":[2,3],"b":[1,-1]}

Expected: -1

Python

def dot_product(a, b):
    """
    Multiply two lists element by element and add up the results.

    Args:
        a, b: lists of numbers of the same length

    Returns:
        The sum of a[0]*b[0] + a[1]*b[1] + ...
    """
    # YOUR CODE HERE
    pass

Run your code to see results

⌘↵ runs against the visible tests

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