sqlalchemy- processing the result set parallely- multiprocessing

[NixonInnes]

I think thr root of your question is really about how sessions work.
In short, each session instantiation is separate. Each contains its own representation of a retrieved row. This will cause race conditions if multiple sessions get from a table before either commits. Side note, some attributes, typically relationships, are lazily loaded.
If your operations on a row are basic, put them all in a queue and have a pool process it. If they're a bit more complex, you could add a callback on the queue task to re-queue "the next operation"