[Python-3000] iostack and Oh Oh

Bill Janssen janssen at parc.com
Fri Dec 1 17:31:15 CET 2006

> Instinctively, I agree with Tomer on this issue. But I'm reasonably
> relaxed about the matter as long as it's optional. What I'm not sure
> about, is if that is the intention. For example,
>     class MyMap:
>         def __getitem__(self, key): ...
>         def __setitem__(self, key, value): ...
> If I pass this into a function (written by a 3rd party, so I have no
> way of changing it) that *only* uses the syntax m[k] on it (never
> needs to do len(m), or m.keys() or anything else), will it work?
> Please note that MyMap is deliberately written to *not* conform to any
> of your proposed base classes.


So long as the third-party function *only* uses m[k] on it (and m[k]
is implemented through __getitem__, as it presumably would be), why
wouldn't it?  I'm not suggesting generic functions which do
interface-based method dispatch (though we may want to do that in the

There could be issues regarding operators, I agree.  For instance, the
[k] operation may be implemented by the Container interface generic
implementation, in which case your type might have to have the
Container interface, which currently means it would have to support
__len__ and __contains__, as well.  But I think that's a separable
discussion, about the locality of operator implementation.


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