[Python-Dev] Proposal: defaultdict

[Guido van Rossum]

On 2/17/06, Adam Olsen <rhamph at gmail.com> wrote:
> > 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.

I'd like to see a real-life example of code that would break this way.
I believe that *most* code that takes a dict will work just fine if
that dict has a default factory.

--
--Guido van Rossum (home page: http://www.python.org/~guido/)