gh-116871: Improve name suggestions in tracebacks

[serhiy-storchaka]

Only include underscored names in name suggestions for AttributeError and ImportError if the original name was underscored.

• Issue: Improve name suggestions for NameError/AttributeError by respecting underscore conventions #116871

[iritkatriel]

I guess you're using [:1] instead of [0] to handle empty strings. But there are no tests for this.

[serhiy-storchaka]

It seems difficult to create tests for this with the current code.

If write wrong_name[0], an IndexError raised for empty wrong_name will be caught by except Exception. If write wrong_name[:1], then any non-empty names will be filtered out in the code below as too different from empty string. In any case the result is the same -- no suggestions.

[gaogaotiantian]

Please take a look at the discussion before merging this. I think ImportError is fine because import is always external use, but AttributeError could be self._private_member which is a perfect valid usage (and arguably a common mistake that could benefit from the name suggestion).