Bug Fix: Do not alter python run-time types

This fixes a bug discovered by Haoran and Callum - if you ask for two different typed collections one after the other, the type propagation system gets very confused because I was accidentally modifying a Python runtime type. This fixes that.

What's Changed

• Do not alter runtime types by @gordonwatts in #120

Full Changelog: 3.2.3...3.2.4