On 07/18/2009 03:32 PM, Chris Rebert wrote:
On Fri, Jul 17, 2009 at 6:54 PM, Michael Lenzen<m.lenzen@gmail.com> wrote: <snip>
New ABCs (abstract base classes) -------------------------------- <snip> Mutable - I think there should be one metaclass for all mutable types just like there is currently Iterable, Sized and Container. We could then check instanceof(obj, Mutable). MutableSequence, MutableSet and MutableMapping would inherit Mutable, or we might be able to just do away with them altogether. There are 3 abstractmethods defined: * pop(self) - This is the simplest to implement, all mutable classes already do. * __setitem__(self, key, value) - This is already implemented for list and dict but would have to be defined for set, more later * __delitem__(self, key) Same as above.
I think this would be better named MutableCollection personally, otherwise it's liable to be confused with the more general mutable vs. immutable types distinction.
<snip>
Extending set to fit the ABCs ----------------------------- I mentioned before that sets don't currently fit into my model. Here are my propositions for the three methods that would need to be implemented. * set.__setitem__(self, elem, value) - Set whether or not elem is in the set based on the boolean evaluation of value. s[elem] = 1 would call s.add(elem) and s[elem] = False would call s.remove(elem), appropriately raising a KeyError if elem not in s. The reason I chose this way is that the only thing you can set about an element of a set is whether or not it is present.
The implicit bool(), which I assume is what you mean by "boolean evaluation", here concerns me, as it could mask bugs where something tries to treat a set like a mapping. I would recommend throwing TypeError if given a non-int and ValueError if given any integer besides 0 or 1, so as to more strongly enforce the set axioms.
Cheers, Chris
Sounds good to me. I changed my implementation and the description on the wiki. I also changed bags to enforce the int restriction. -Lenzen