Question

I am writing my own function for parsing XML text into objects which is can manipulate and render back into XML text. To handle the nesting, I am allowing XML objects to contain other XML objects as elements.

Since I am automatically generating these XML objects, my plan is to just enter them as elements of a dict as they are created. I was planning on generating an attribute called name which I could use as the key, and having the XML object itself be a value assigned to that key.

All this makes sense to me at this point. But now I realize that I would really like to also save an attribute called line_number, which would be the line from the original XML file where I first encountered the object, and there may be some cases where I would want to locate an XML object by line_number, rather than by name.

So these are my questions:

1. Is it possible to use a dict in such a way that I could find my XML object either by name or by line number? That is, is it possible to have multiple keys assigned to a single value in a dict?
2. How do I do that?
3. If this is a bad idea, what is a better way?

Answer 1

Yes, it is possible. No special magic is required:

In [1]: val = object()

In [2]: d = {}

In [3]: d[123] = val

In [4]: d['name'] = val

In [5]: d
Out[5]: {123: <object at 0x23c6d0>, 'name': <object at 0x23c6d0>}

I would, however, use two separate dictionaries, one for indexing by name, and one for indexing by line number. Even if the sets of names and line numbers are completely disjoint, I think this is a cleaner design.