[Python-Dev] Proposal: defaultdict (original) (raw)

Adam Olsen rhamph at gmail.com
Fri Feb 17 23:56:24 CET 2006

On 2/17/06, Guido van Rossum <guido at python.org> wrote:

On 2/17/06, Adam Olsen <rhamph at gmail.com> wrote: > It's also makes it harder to read code. You may expect d[key] to > raise an exception, but it won't because of a single line up several > pages (or in another file entierly!)

Such are the joys of writing polymorphic code. I don't really see how you can avoid this kind of confusion -- I could have given you some other mapping object that does weird stuff.

You could pass a float in as well. But if the function is documented as taking a dict, and the programmer expects a dict.. that now has to be changed to "dict without a default". Or they have to code defensively since d[key] may or may not raise KeyError, so they must avoid depending on it either way.

-- Adam Olsen, aka Rhamphoryncus

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