En Sat, 28 Nov 2009 06:30:44 -0300, Joshua Bronson <jabron...@gmail.com>
escribió:
On Nov 27, 9:36 pm, "Gabriel Genellina" <gagsl-...@yahoo.com.ar>
wrote:
En Fri, 27 Nov 2009 15:12:36 -0300, Francis Carr
<coldtort...@gmail.com> escribió:
> After much tinkering, I think I have a simpler solution. Just make
> the inverse mapping accessible via an attribute, -AND- bind the
> inverse of -THAT- mapping back to the original. The result is a
> python dict with NO NEW METHODS except this inverse-mapping
> attribute. I have posted it on code.activestate.com as <a
> href="http://code.activestate.com/recipes/576968/";>Recipe 576968:
> Flipdict -- python dict that also maintains a one-to-one inverse
> mapping</a>
Just a couple of comments:
Instead of:
self._flip = dict.__new__(self.__class__)
I'd write:
self._flip = self.__class__()
unless I'm missing something (but see the next point).
How would this not cause infinite recursion?
That goes under "unless I'm missing something" ;)
You're right, it would cause infinite recursion. Not a good idea...
Also, although Python's GC is able to handle them, I prefer to avoid
circular references like those between x and x._flip. Making
self._flip a weak reference (and dereferencing it in the property)
should be enough.
If both self._flip and self._flip._flip are weak references, no strong
references to the inverse mapping survive leaving the constructor
scope. Unless I'm missing something, only one of these can be a weak
reference, and then you'd have to do something like this in the
property to prevent "TypeError: FlipDict is not callable":
@property
def flip(self):
try:
# we're an inverse, self._flip is a weak reference
return self._flip()
except TypeError:
# we're a forward mapping, self._flip is a strong
reference
return self._flip
Yes - although I'd explicitely test for a weakref object:
def flip(self):
_flip = self._flip
if isinstance(_filp, weakref.ref):
return _flip()
return _flip
and probably all those internal references to self._flip should become
self.flip too; I've not tested the code but I think it *should* work...
--
Gabriel Genellina
--
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