>>> import importlib.util>>> importlib.util.resolve_name(".submodule", None)Traceback (most recent call last):  File "<stdin>", line 1, in <module>  File "/home/proj/python/cpython/Lib/importlib/util.py", line 26, in resolve_name    '(no leading dot)'.format(name))ValueError: '.submodule' is not a relative name (no leading dot)This message sounds like nonsense. Perhaps the it should say something like:    '.submodule' should be an absolute name (no leading dot)or:    relative import of '.submodule' not allowed outside of a package

So both proposed messages are correct depending on what you want to accomplish; it all depends on whether the leading dot was the mistake or the missing package was.And the message does make some sense if you read it more like "'.submodule' is not a relative name (drop the leading dot)". I do agree, though, it's hard to read as written.

New changesetb3a0765671d6 by Brett Cannon in branch 'default':Issue#25771: Tweak ValueError message when package isn't specifiedhttps://hg.python.org/cpython/rev/b3a0765671d6

Fixed in default (left 3.5 alone since it technically isn't a bug fix but a clarification; fine if someone else wants to handle the backport).

Thanks, the fix is fine and there is no big need to backport it. For the record, I only came across this playing with runpy. Old message:$ python3 -m .submodule/sbin/python3: Error while finding spec for '.submodule' (<class 'ValueError'>: '.submodule' is not a relative name (no leading dot))New message:$ ./python -m .submodule/media/disk/home/proj/python/cpython/python: Error while finding spec for '.submodule' (<class 'ValueError'>: no package specified for '.submodule' (required for relative module names))