Python API exposure mechanisms (public/internal) - determining status quo

Motivation and scope This is a summary of the API exposure mechanisms currently used in Python, i.e. whether interaction with names from outside of the namespace they live in is intended and supported. The primarily relevant namespaces are modules and classes, but the exposure mechanisms are described independently of namespace type where possible. This is modivated from apparently different understandings of the status-quo in the discussion threads on PEP 842-844, and specifically triggered t...