“The maps are immutable, immortal and reused as much as possible. This means, that two instances of the same class with the same set of attributes will have the same map. This also means that the memory the map itself uses is not too important, because it will potentially be amortized over many instances.”
“[…] importing a submodule will actually modify the parent module’s
namespace. […] This happens even if you do not get an explicit
reference to x, eg if you do
import x.y as t.”
Ingenious example in “Guideline: Use mock objects …”.