[zubat]

I ended up making a custom data structure and query language around this kind of notation. Not in Python(am working in Haxe) but easily generalized. The structure is either array or string map or ordered string map with a dynamic data field and optional string tags. So it maps very well onto JSON or XML style data, but comes with the benefit of a very unambiguous way to do queries, where I can mix together addressing styles(take this numbered index OR take the named key) and pull elements into an array without much difficulty. The lookup syntax is "@<key>#<index>..." and each key or index entry is parsed into an ADT. I can pass along partially constructed queries as the relevant data to be processed. It's not quite as flexible as SQL since the data has to come in tree form, but it creates a major design affordance: the same query can be passed to a custom algorithm or custom data structure, with less ambiguity than a simple string lookup.

To some extent this retreads ground covered by e.g. XPath, but the specific structure puts it closer to my day-to-day needs.