The new 2.3 version of TurboGears2 is aiming at providing a great toolkit on both Python3 and Python2 for such cases thanks to builtin support for:
New minimal mode for small single file applications.
Gevent based deploy on Mozilla Circus using the new GearBox toolkit
The TGJSonAutodoc sphinx extension for automatically documenting JSON based API
Out of the box support for MongoDB using the Ming ODM
The DebugBar profiler and query analyzer for MongoDB
Those tools can make really easy to quickly prototype a fully working and documented web service, greatly improving a developer life and quality of the services. Even deployment can become a single line command thanks to the GearBox toolkit integration with Mozilla Circus while the jsoncall sphinx extension can really speed up service documentation thanks to its tgjsonautodoc directive.