import sys

class Mod(object):
    def __getattr__(self, name):
        print(name)
        raise AttributeError

foobar = type(sys)('foobar')

sys.modules['foobar'] = foobar
sys.modules['foobar.baz'] = Mod()

from foobar.baz import x
# CPython <= 3.4: ImportError
# CPython 3.5b2+ 58ded1d9a3c1: AttributeError