When the globals argument to importlib.__import__() contained any value for

__package__, it was used. This was incorrect since it could be set to None to
represent the fact that a proper value was unknown. Now None will trigger the
calculation for __package__.

Discovered when running importlib against test_importhooks.

Lib/importlib/_bootstrap.py

@@ -922,10 +922,10 @@ def __import__(name, globals={}, locals={}, fromlist=[], level=0):
     if level == 0:
         module = _gcd_import(name)
     else:
-        # __package__ is not guaranteed to be defined.
-        try:
-            package = globals['__package__']
-        except KeyError:
+        # __package__ is not guaranteed to be defined or could be set to None
+        # to represent that it's proper value is unknown
+        package = globals.get('__package__')
+        if package is None:
             package = globals['__name__']
             if '__path__' not in globals:
                 package = package.rpartition('.')[0]

Lib/importlib/test/import_/test___package__.py

@@ -19,8 +19,9 @@ class Using__package__(unittest.TestCase):
           base = package.rsplit('.', level)[0]
           return '{0}.{1}'.format(base, name)
 
-    But since there is no guarantee that __package__ has been set, there has to
-    be a way to calculate the attribute's value [__name__]::
+    But since there is no guarantee that __package__ has been set (or not been
+    set to None [None]), there has to be a way to calculate the attribute's value
+    [__name__]::
 
       def calc_package(caller_name, has___path__):
           if has__path__:
@@ -43,17 +44,22 @@ class Using__package__(unittest.TestCase):
                                             fromlist=['attr'], level=2)
         self.assertEquals(module.__name__, 'pkg')
 
-    def test_using___name__(self):
+    def test_using___name__(self, package_as_None=False):
         # [__name__]
+        globals_ = {'__name__': 'pkg.fake', '__path__': []}
+        if package_as_None:
+            globals_['__package__'] = None
         with util.mock_modules('pkg.__init__', 'pkg.fake') as importer:
             with util.import_state(meta_path=[importer]):
                 import_util.import_('pkg.fake')
-                module = import_util.import_('',
-                                 globals={'__name__': 'pkg.fake',
-                                          '__path__': []},
+                module = import_util.import_('', globals= globals_,
                                                 fromlist=['attr'], level=2)
             self.assertEquals(module.__name__, 'pkg')
 
+    def test_None_as___package__(self):
+        # [None]
+        self.test_using___name__(package_as_None=True)
+
     def test_bad__package__(self):
         globals = {'__package__': '<not real>'}
         with self.assertRaises(SystemError):

Misc/NEWS

@@ -68,6 +68,9 @@ C-API
 Library
 -------
 
+- When the globals past to importlib.__import__() has __package__ set to None,
+  fall back to computing what __package__ should be instead of giving up.
+
 - Raise a TypeError when the name of a module to be imported for
   importlib.__import__ is not a string (was raising an
   AttributeError before).