Asserts in module code

[DocOtak]

I noticed some assert statements in wod.py specifically:

• wod.py:36
• wod.py:454

assert statements are not checked if __debug__ is set to False. While the default for __debug__ is True, this may not always be the case. See:
https://docs.python.org/2/reference/simple_stmts.html#assert

These should probably be replaced with actual if then raise statements.