Summary

If a module defines the symbol__all__, that definition should be used when doing a wildcard import: all listed symbols and no others should be added to the parent global environment. This is the standard in CPython.

This pull requests fixes a longtimeFIXME inmp_parse_all to implement this behaviour.

Each item is loaded in the same way as if it would be an explicit import statement, including invoking the the module's__getattr__ function if needed. This provides a straightforward solution for fixing star import of modules using a dynamic loader, such asextmod/asyncio (see issue#7266, dated 2022).

Testing

The corresponding test cases have been added totests/import, including the default behaviour when__all__ is not defined.

As star imports are not expected to be useful on systems with very limited ressources, this improvement is only enabled for ports at BASIC_FEATURES level. In order to skip the new test cases on builds at lower feature level, the test file checks for the availability of another feature enabled at the same level (next's 2nd argument).

Trade-offs and Alternatives

This improvement will slightly increase the code size, for the sake of CPython compatibility.

On the other hand, limiting imports to a subset of symbols rather than importing most of them in the parent globals will be reduce RAM usage. The feature also fixes a longstanding issue with dynamic loading of modules, which is another method used to reduce RAM usage.