Quoting skip@pobox.com:

>
>     Guido> Over lunch with Alex Martelli, he proposed that a subclass of
>     Guido> dict with this behavior (but implemented in C) would be a good
>     Guido> addition to the language.
>
> Instead, why not define setdefault() the way it should have been done in the
> first place?  When you create a dict it has the current behavior.  If you
> then call its setdefault() method that becomes the default value for missing
> keys.
>
>     d = {'a': 1}'
>     d['b']              # raises KeyError
>     d.get('c')          # evaluates to None
>     d.setdefault(42)
>     d['b']              # evaluates to 42
>     d.get('c')          # evaluates to 42
>
> For symmetry, setdefault() should probably be undoable: deldefault(),
> removedefault(), nodefault(), default_free(), whatever.

Well, first not ot break the current interface, and second because I think it
reads better I would prefer :

      d = {'a': 1}'
      d['b']              # raises KeyError
      d.get('c')          # evaluates to None
      d.default = 42
      d['b']              # evaluates to 42
      d.get('c')          # evaluates to 42

And to undo the default, you can simply do :

      del d.default

And of course, you can get the current value :

      d.default

But then, as proposed many times, I would rather see a function call. Like :

    d.default = lambda key: 42

The argument of the function is the current key. It would allow things 
like that
:

    d.default = time_comsuming_operation

where time_comsuming_operation get a single argument.

>
> The only question in my mind is whether or not getting a non-existent value
> under the influence of a given default value should stick that value in the
> dictionary or not.
>
> down-with-more-builtins-ly, y'rs,
>
> Skip
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