Summarising Numbers

Totals, averages and extremes, and what each one hides.

The three you reach for first

sum, len and max answer most questions about a column. The average is sum divided by len, and it is worth writing out once so you remember it can divide by zero.

scores = [92, 88, 79]
print(sum(scores))
print(sum(scores) / len(scores))
print(max(scores))

An average is not the whole story

The same average can come from very different data. Reporting it next to the smallest and largest value costs one line and prevents most of the misreadings.

a = [50, 50, 50]
b = [0, 50, 100]
print(sum(a) / len(a), sum(b) / len(b))
print(min(b), max(b))

Exercise

Try It Yourself

Write a function average(scores) that returns the mean, and returns 0 for an empty list rather than raising.

def average(scores):
    # Return the mean, or 0 when there is nothing to average.
    return None

print(average([92, 88, 79]))

Press Run to see output

Check Your Understanding

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