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I found the problem. _frozen_importlib is being loaded by C code which is using the equivalent of _imp.init_frozen(). importlib.machinery.FrozenImporter is doing a more controlled, manual approach of using _imp.get_frozen_object() and then initializing the module itself. Problem is that the former sets __file__ to '<frozen>' and the latter doesn't; this was an unintended side-effect of updating FrozenImporter for PEP 451 as this was the only way to make exec_module() work w/o serious C hacking. You can see the difference this way:
 >>> import _imp
 >>> __hello__again = _imp.init_frozen('__hello__')
 Hello world!
 >>> __hello__again.__spec__.has_location
 Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 AttributeError: 'NoneType' object has no attribute 'has_location'
 >>> __hello__again.__file__
 '<frozen>'
compared to:
 >>> import __hello__
 Hello world!
 >>> __hello__.__spec__.has_location
 False
 >>> __hello__.__spec__.origin
 'frozen'
 >>> __hello__.__file__
 Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 AttributeError: 'module' object has no attribute '__file__'
The clean solution is to fix PyImport_ImportFrozenModuleObject() to stop setting __file__ and then fix importlib/__init__.py to deal with the lack of file path (this should implicitly fix _frozen_importlib when it's __spec__ is set in _setup). The more backwards-compatible would be to toss '<frozen>' back in for __spec__.origin and set __spec__.has_location to True which is all semantically wrong.
I vote for the clean solution along with a backported note into What's New.