support for __all__ filtering with from ... import *

[jbrelwof]

• Fixes support for __all__ with from ... import * #10516.

Circuitpython does not support filtering from someModule import * when someModule contains __all__ = ['symbol1', 'symbol2', ...]. This results in importing more symbols than intended, which can cause a little wasted memory (entries in the globals() in the scope containing from someModule import * ) and differs from CPython in ways that can introduce subtle bugs (primarily through unexpected replacement of existing symbols).

This includes an enhanced mp_import_all(...) in py/runtime.c to support from ... import * filtering when __all__ = [...] is present.

I have basic tests (which it passes) for the following:

• import is actually filtered (non-_private symbols not contained in __all__ are not imported)
• values of type other than string in __all__ will throw TypeError
• undefined entries in __all__ (i.e. __all__ = ['hello','world'] where world is undefined) will throw AttributeError

but I'm not sure where/how to add them so they become part of the CircuitPython CI testing pipeline

I also have a few things that I got "working" through trial and error which might have more efficient / recognizable patterns available. For example:

• iterating values in __all__
• getting string value of __all__ for lookup key
• optional (conditionally compiled) debug output
• raising exceptions
• ... ???

[dhalbert]

Since this is fixed by micropython#17331, we could wait for that. We will be merging from MicroPython when V1.26 comes out.