The idea, obviously, is for python -m idlelib to also work on all systems.  When this was requested as part of the discussion on another issue, I thought there was no idlelib.__main__ because __main__ did not work on 2.7.  Someone corrected me and the expectation of me and others was that the absence was just an easily corrected oversight.  Turns out not so.  I wanted to at least document that the backport is not trivial.  I am rather curious why the same code behaves so differently on 2.7.