This is a Python-based reference implementation of the happy numbers coding exercise. 
It is unoptimized.

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### Problem Statement

A happy number is a number defined by the following process: Starting with any positive integer, replace the number with the sum of the squares of its digits, and repeat the process until the number either equals 1 (where it will stay), or it loops endlessly in a cycle that does not include 1. Those numbers for which this process ends in 1 are happy numbers, while those that do not end in 1 are unhappy numbers (or sad numbers).

For example, 19 is happy, as the associated sequence is:

1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1.

The first five happy numbers are 1, 7, 10, 13, 19.

Print the happy numbers up to 1,000. Hint: There are 143.