I need to get a list of a model\'s properties which are actually relationships (that is, they were created by relationship()).
Say I have a model
There is indeed - take a look at sqlalchemy.inspection.inspect. Calling inspect on a mapped class (for example, your Thing class) will return a Mapper, which has a relationships attribute that is dict like:
from sqlalchemy.inspection import inspect
thing_relations = inspect(Thing).relationships.items()