Hendrik van Rooyen wrote:
>
> "7stud" <[EMAIL PROTECTED]> wrote:
>
>
>>.......... But using a tuple as a
>>key in a dictionary is probably something you will never do.
>
>
> Yikes! I do this all the time...
>
> Think of an address in any one town.
> It has a Street, and a number
> (could be more complex, like a sub number for an apartment
> in a block, but lets ignore that for now)
>
> so:
> addy = ("First Avenue", 10)
> Residents = {addy:"Frank Everyman",......}
>
> To make a thing where you can look up who lives at a place...
> (this is simplistic of course, for illustrative purposes - few people
> live completely alone. - it should be at least a list, or possibly a dict
> by surname...)
>
> I find that when I do this, I almost invariably also create the
> inverse dict:
>
> Addresses = {"Frank Everyman":addy,.....}
>
> So that you can get at stuff from all directions. If you keep it
> up you have a home made relational database if you are not careful...
>
> But if you limit it to one thing and its inverse, its quite useful, and it
> would be nice to have one "doubledict" that can be accessed as speedily
> from either end...
>
> Sort of an internally linked list of mixed hashed immutables, where:
>
> doubledict["Frank Everyman"] yields addy, and
> doubledict[addy] yields "Frank Everyman"
>
> It would have direct applicability in things like the label table in
> an assembler, for debugging and so on.
>
> - Hendrik
>
I'm thinking that, to avoid big a lot of ambiguity, such a double dict
would need to be implemented as two distinctly referenced data structures:
class DD(object):
def __init__(self, adict):
self._fwd = {}
self._fwd.update(adict)
self._bkwk = dict(v,k for k,v in adict.items())
def fwd(self, k)
return self._fwd[k]
def bkwd(self, k)
return self._bkwd[k]
def __setitem__(self, k, v):
self._fwd[k] = v
self._bkwd[v] = k
def __getitem__(self, k):
if (k in self._fwd) and (k in self._bkwd):
raise KeyError, 'Which do I look in first?'
else:
raise KeyError, 'Too much guesswork. Use fwd() or bkwd().'
James
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