Here's what I feel is a nearly complete patch. The only outstanding issues that I feel need to be answered are 4 spots where calls into the interpreter may result in unexpected changes to the object or make the current function state out-of-date.
1. _odict_clear_nodes() while iterating over the nodes.
2. _odict_keys_equal() while iterating over the nodes.
3. odict_sizeof() -- I'm not too worried about this one.
4. _odict_copy() while iterating over the nodes.
Once I feel comfortable with some resolution for those, I'm going to consider the patch ready to go, pending reviews.