Why keep identity-based equality comparison?

[Steven Bethard]

Mike Meyer wrote:
> spam.noam at gmail.com writes:
> 
>> My question is, what reasons are left for leaving the current default
>> equality operator for Py3K, not counting backwards-compatibility?
>> (assume that you have idset and iddict, so explicitness' cost is only
>> two characters, in Guido's example)
> 
> Yes. Searching for items in heterogenous containers. With your change
> in place, the "in" operator becomes pretty much worthless on
> containers of heterogenous objects. Ditto for container methods that
> do searches for "equal" members. Whenever you compare two objects that
> don't have the same type, you'll get an exception and terminate the
> search. If the object your searching for would have been found
> "later", you lose - you'll get the wrong answer.

Not to advocate one way or the other, but how often do you use 
heterogeneous containers?  I couldn't find any in my (admittedly small) 
codebase.  Could you post some examples of what kind of problems lend 
themselves to being solved by heterogeneous containers?

Thanks,

STeVe