Storing 'unhashable' types in dictionaries by address

[Mel Wilson]

In article <l1u1bjgg3d.fsf at budvar.future-i.net>,
Ed Avis <ed at membled.com> wrote:
>A dictionary requires that its key type be hashable.  This means you
>cannot use lists as keys of a dictionary.  Is there any way round
>this?
>
>I would like to store some 'extra' information associated with some
>lists, but do so outside the lists themselves.  For example this is
>what I would like to write:
>
>l0 = ['strawberry']
>l1 = ['mint', 'choc']
>l2 = ['vanilla', 'liver']
>
># This dictionary stores some extra comments on each flavour.
>d = {}
>d[l0] = 'yum'
>d[l1] = 'so-so'
>d[l2] = 'ugh'
>
>print d[l0]    # prints 'yum'
>l0.append(55)
>print d[l0]    # still prints 'yum', since it's the same list
>
># Now I construct a new list which, although it contains the same
># strings as l1, is a different object.  This is just to demonstrate
># that d indexes by 'is' rather than by ==.
>#
>new_list = ['mint', 'choc']
>print new_list in d.keys()    # prints 0, or false
>
>
>I hope the intent is clear - I want to look up by object identity and
>not by the contents of the list.

Just store and look up the lists by object identity:

d[id(l0)] = 'yum'

print d[id(l0)]

and so on.

        Regards.        Mel.