On 15/03/2011 19:57, Greg Ewing wrote:
Nick Coghlan wrote:
The challenge here is how it would interact with inheritance. pydoc
couldn't use normal attribute lookup, it would have to walk the MRO
manually,
This is an instance of a pattern that I've encountered a
few times in things that I've done: you have a class
attribute containing a list of things, and you want it
to be "additive" with respect to inheritance -- i.e. it
contains the items specified in a particular class plus
all those specified in its base classes.
This can obviously be arranged using appropriate metaclass
hackery, but I'm wondering whether it could be provided
using some mechanism that can be applied orthogonally
to any class attribute.
Right, I recently came across a similar usecase where a class needed to
extend an object defined in a base class. What we *wanted* to do was the
following:
class Foo(object):
thing = Thing()
class Bar(Foo):
thing.baz = 3
This doesn't work for obvious reasons. One potential solution was
re-assigning 'thing' on Bar as well and using a metaclass to merge them.
I think we ended up doing this, which is *slightly* ugly but not too bad:
class Bar(Foo):
thing = Foo.thing
thing.baz = 3
All the best,
Michael
Maybe this is another reason to have a hook somewhere
in the standard class creation process that allows a
descriptor to initialise itself with knowledge of its
environment.
--
http://www.voidspace.org.uk/
May you do good and not evil
May you find forgiveness for yourself and forgive others
May you share freely, never taking more than you give.
-- the sqlite blessing http://www.sqlite.org/different.html
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