homepage

http://hg.python.org/cpython/file/aba513307f78/Lib/importlib/_bootstrap.py#l974
 974 # The hell that is fromlist ...
 975 if not fromlist:
 976 # Return up to the first dot in 'name'. This is
complicated by the fact
 977 # that 'name' may be relative.
 978 if level == 0:
 979 return sys.modules[name.partition('.')[0]]
 980 elif not name:
 981 return module
 982 else:
 983 cut_off = len(name) - len(name.partition('.')[0])
 984 return sys.modules[module.__name__[:-cut_off]]
If level is 0, should name == module.__name__?
Yes.
 
If so, then I think that simplifies to
 if not name:
 return module
 genericname=module.__name__.rpartition(".")[0]
 return sys.modules[genericname]
Seems right. Can you file a bug and assign it to me?

So I simply swapped out the code and the tests fail. Then I realized why: while the assumption is right, that does not mean that that name passed to __import__() isn't relative and thus shifts what need to be returned (the else clause case). That's why it's a slice off of __name__ based on name itself; name is some funky tail section of __name__ for relative imports.