Can dictionary values access their keys?

[Scott David Daniels]

Matthew Thorley wrote:
> This may be a very rudimentary question, but here goes:
 From your questions, I believe you are not thinking of values as
being distinct from the names and data structures that refer to them.

What is the parent of 23 in the following expression?

     1 + 11 * 2

If you know that, what is the parent of 293 in the same expression?

> If I have a simple dictionary, where the value is a class or function,
> is there an interface through which it can discover what its key is?
> Similar to index() for list.

     def keyfor(dictionary, element):
         for key, value in dictionary.iteritems():
             if value == element:  # value is element if identity quest
                 return key
         raise ValueError, element

> On a similar note, if one object is part of another, 
This is the idea you have wrong.  In C, C++, Java, and Fortran you
might have objects part of other objects, but in Python objects refer
to each other.

How about this:

     class Holder(object): pass

     v = [1 + 11 * 2]
     w = [1, v, 3]
     d = {1: v}
     o = Holder()
     o.x = v

What is the parent of v?

Or even worse:

     v = [1]
     v[0] = v

What is the parent of v now?

--Scott David Daniels
Scott.Daniels at Acm.Org