I suggest we write examples for every function like:
<code>
def add:
  '''
  >>> add(1, 2)
  3
  >>> add(1, 1)
  2
  '''
</code>

This way the code can be more readable and we can run <code>python -m doctest ArabyStatistics.py</code>
and it will print an error message if any example doesn't return the expected result.

You could try it know, change the expected result for one example and run the above command and see what happens.