verify the return value of a function

[Mel Wilson]

Jean-Michel Pichavant wrote:

> isinstance is fine, if you could find the source where it is
> discouraged... Could be a consequence of some specific context.
> However, checking types in OOP is in general a failure. Unitary tests
> are possibly an exception.

I think it's discouraged when people try to write big overloaded functions 
that check the types of the arguments to decide what they should be doing.
In diagnostics and tests like the OP's there should be no problem.

	Mel.