[Python-Dev] Proposal: defaultdict

Adam Olsen rhamph at gmail.com
Sat Feb 18 20:06:59 CET 2006

On 2/18/06, James Y Knight <foom at fuhm.net> wrote:
> On Feb 18, 2006, at 2:33 AM, Martin v. Löwis wrote:
> > Well, as you say: you get a KeyError if there is an error with the
> > key.
> > With a default_factory, there isn't normally an error with the key.
> But there should be. Consider the case of two servers. One which
> takes all the items out of the dictionary (using items()) and puts
> them in some other data structure. Then it checks if the "Date"
> header has been set. It was not, so it adds it. Consider another
> similar server which checks if the "Date" header has been set on the
> dict passed in by the user. The default_factory then makes one up.
> Different behavior due to internal implementation details of how the
> server uses the dict object, which is what the restriction to
> _exactly_ dict prevents.

It just occured to me, what affect does this have on repr?  Does it
attempt to store the default_factory in the representation, or does it
remove it?  Is it even possible to store a reference to a builtin such
as list and have eval restore it?

Adam Olsen, aka Rhamphoryncus

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