[Python-ideas] should `dict` supply a default `__missing__` implementation?

[Ethan Furman]

On 06/29/2016 12:09 PM, Guido van Rossum wrote:

> So providing the comprehensive base class is up to the user, not up to
> the stdlib. Is that such a big deal?

No, it's not.  But it makes for a better user experience if the base 
class has the __missing__ method that raises a KeyError already.

Didn't we add a UserDict that could be subclassed primarily because 
subclassing dict directly was such a poor user experience?

If adding __missing__ to dict is huge (performance hit?), we don't do 
it.  If it's not, I think we should.  Maybe add it to UserDict if 
performance is a concern?

--
~Ethan~