Yep, this fixes the circular import problem from #8983.

I was just reading this code myself to see how to fix it. My thought was to delay creation of _KNOWN_TYPES by defining

_KNOWN_TYPES = None
def _get_known_types():
    global _KNOWN_TYPES

    if _KNOWN_TYPES is not None:
        return _KNOWN_TYPES

    ... (indented definition of _KNOWN_TYPES goes here ...

but I haven't properly thought through all the performance implications that you probably know about.

This PR looks good to me, let's just wait for tests to pass.

The __main__ clause doesn't seem to work:

python2 ./getlimits.py 
Traceback (most recent call last):
  File "./getlimits.py", line 10, in <module>
    from .machar import MachAr
ValueError: Attempted relative import in non-package

(the other files in this directory which have such a clause work properly).

The main clause doesn't seem to work:

Should be removed. Scripts cannot use absolute_imports as they do not run in the right context. That clause dates back to 2006 and was probably used for debugging.

Thanks Matthew. I expect we can do more in this regard, but this is a good start and fixes the immediate problem.

Thanks for moving this one forward @charris, and thanks for the fix @matthew-brett