Dictionary, keys and alias

[Steven D'Aprano]

On Mon, 18 Jul 2005 12:17:37 +0200, Glauco wrote:

> I want to insert a concept of alias in a dict_based class.
> 
> The idea  is to have a facoltative name in the same dict that correspond 
> at the same value. With this alias i can change original value.
> 
> example:
> 
> mydict['a'] = 1
> I must define an alias  example: myFunctAlias( mydict, 'a', 'b')
> print mydict
> {'a':1, 'b':1}
> mydict['b'] = 2
> print mydict
> {'a':2, 'b':2}
> 
> 
> The only idea i have is to implement two dictionary one for convert 
> name, alias in two keys with the same value (eg.numeric) in the first 
> dict. The second for store only one time the k, v .

You need some sort of redirection, something like this (untested):

class Doubledict:
    def __init__(self, **kargs):
        self.data = {}
        self.aliases = {}
        for key in kargs:
            # Point the key to a hash.
            self.aliases[key] = hash(key)
            # And point the hash at the value.
            self.data[hash(key)] = kargs[key]

    def setalias(self, key, alias):
        # Point the alias to the same hash as the real key.
        self.aliases[alias] = hash(key)

    def __getitem__(self, key):
        return self.data[self.aliases[key]]

    def __setitem__(self, key, value):
        self.data[self.aliases[key]] = value


The only niggly worry I have is I'm not sure when hash can be used, when
it is unique, or even if is it guaranteed to be unique.

-- 
Steven.