Thoughts on object representation in a dictionary

[py]

Say I have classes which represent parts of a car such as Engine, Body,
etc.  Now I want to represent a Car in a nested dictionary like...

{string_id:{engine_id:engine_object, body_id:body_object}}....ok?

Well the other thing is that I am allowed to store strings in this
dictionary...so I can't just store the Engine and Body object and later
use them.  ....this is just a requirement (which i dont understand
either)...but its what I have to do.

So my question is there a good way of storing this information in a
nested dictionary such that if I receive this dictionary I could easily
pull it apart and create Engine and Body objects with the information?
Any suggestions at all?  keep in mind I am limited to using a
dictionary of strings...thats it.

Thanks for any input.