Tim Peters wrote:

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-1. User input is never trustworthy. Your and your users' software lives will be a lot happier if you stick to the rule that an assertion failure always (always!) announces a bug in the implementation -- assertion failure is never a user's fault.

So you prefer

if __debug__ and node.nodeType!=ELEMENT_TYPE: raise TypeError

Unfortunately there's no way to turn that off at "compile time" so you always incur the __debug__ lookup cost. That would send us back to two versions of the methods.

Maybe testing would indicate that the performance implications are minor. If so, I wouldn't mind having the type checks in there.

Of course, continuations would be perfect here, as one could set the continuation to resume after the check if he wished to bypass it. Something tells me I should duck now... not-very-seriously-mind-you'ly yrs -- Uche Ogbuji Principal Consultant uche.ogbuji@fourthought.com +1 303 583 9900 x 101 Fourthought, Inc. http://Fourthought.com 4735 East Walnut St, Ste. C, Boulder, CO 80301-2537, USA Software-engineering, knowledge-management, XML, CORBA, Linux, Python