Puzzle 18 Round and Round We Go

Python Brain Teasers — by Miki Tebeka (27 / 40)

👈 Endgame | TOC | TF (Without IDF) 👉

round.py

​ ​print​(round(1.5), round(2.5))

Guess the Output

IMPORTANT

Try to guess what the output is before moving to the next page.

This code will print: 2 2

Rounding seems easy. round(1.1) evaluates to 1. round(1.8) evaluates to 2. The question is, how do you round the .5 numbers? Should you round up? Down? Turns out, there are a lot of ways to do it.

Python 3 uses bankers’ rounding. Odd numbers are rounded up; even numbers are rounded down. The reasoning behind this method is that if you round a list of numbers, assuming there’s roughly the same number of odd and even numbers, the error (rounding) will cancel each other.

Python 2 uses a different method called round away from zero. If you run this teaser in Python 2, you’ll see (2.0, 3.0) as the output.

Further Reading