On Friday I checked in changes to butler that add a Repository
class, and allow butler to be instantiated using a nested dictionary that describes the butler configuration including what mapper to use, mapper policy, what storage type to use, etc.
Documentation that describes these things is in LDM-463. It’s not in master yet, but you can read the version in the ticket branch at http://ldm-463.lsst.io/en/tickets-dm-5091/
Of note are sections 2.3 Repository and 2.7 Butler Configuration
Please let me know if you have any questions/comments/etc.