An example of python doctest

doctest_example.py

def factorial(number):
    """Return the factorial of the parameter 'number'

    :number: an int object.
    :returns: an int object.

    >>> factorial(5)
    120
    """
    return ((number <= 1 and 1) or number * factorial(number - 1))

To test it, just run:

$ python -m doctest doctest_example.py