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Yes, I found that. The line in question is, however, this:
 _verbose_message('import {!r} # {!r}', name, loader)
(_bootstrap.py:1254).
Unfortunately, I see no way to get at the line from which the import occurred here. The loader itself is not useful for that. Perhaps the author of importlib knows more, e.g. whether the feature to know whence an import originates is useful or has been dropped.