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[Python-Dev] Proposal: defaultdict

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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