The bugs with the random tests when using Python, described below, still seem to be present.

Your toString() method should be called:

def __str__(self)

See https://docs.python.org/2/reference/datamodel.html#object.__str__

When I Run Tests they all pass, but when I try to Submit I fail on the 10th test.

Priting out the test MongoIDs and the function being called gives:

is_valid:
s = 333333333333333333333333
Test Passed
is_valid:
s = 333333333333333333333333
True should equal False

So the 9th test seems to be identical to the 10th test, but one passes and the other doesn't.

Am I missing something?