Issue #25791: Raise an ImportWarning when __spec__ or __package__ are

not defined for a relative import.

This is the start of work to try and clean up import semantics to rely
more on a module's spec than on the myriad attributes that get set on
a module. Thanks to Rose Ames for the patch.

2 files changed, 32 insertions, 14 deletions

diff --git a/Lib/importlib/_bootstrap.py b/Lib/importlib/_bootstrap.py
index 6f62bb3..9adcf7b 100644
--- a/Lib/importlib/_bootstrap.py
+++ b/Lib/importlib/_bootstrap.py
@@ -1032,8 +1032,14 @@ def _calc___package__(globals):
     to represent that its proper value is unknown.
 
     """
+    spec = globals.get('__spec__')
+    if spec is not None:
+        return spec.parent
     package = globals.get('__package__')
     if package is None:
+        _warnings.warn("can't resolve package from __spec__ or __package__, "
+                       "falling back on __name__ and __path__",
+                       ImportWarning, stacklevel=3)
         package = globals['__name__']
         if '__path__' not in globals:
             package = package.rpartition('.')[0]
diff --git a/Lib/test/test_importlib/import_/test___package__.py b/Lib/test/test_importlib/import_/test___package__.py
index c7d3a2a..08e41c9 100644
--- a/Lib/test/test_importlib/import_/test___package__.py
+++ b/Lib/test/test_importlib/import_/test___package__.py
@@ -33,31 +33,39 @@ class Using__package__:
 
     """
 
-    def test_using___package__(self):
-        # [__package__]
+    def import_module(self, globals_):
         with self.mock_modules('pkg.__init__', 'pkg.fake') as importer:
             with util.import_state(meta_path=[importer]):
                 self.__import__('pkg.fake')
                 module = self.__import__('',
-                                            globals={'__package__': 'pkg.fake'},
+                                            globals=globals_,
                                             fromlist=['attr'], level=2)
+        return module
+
+    def test_using___package__(self):
+        # [__package__]
+        module = self.import_module({'__package__': 'pkg.fake'})
         self.assertEqual(module.__name__, 'pkg')
 
-    def test_using___name__(self, package_as_None=False):
+    def test_using___name__(self):
         # [__name__]
-        globals_ = {'__name__': 'pkg.fake', '__path__': []}
-        if package_as_None:
-            globals_['__package__'] = None
-        with self.mock_modules('pkg.__init__', 'pkg.fake') as importer:
-            with util.import_state(meta_path=[importer]):
-                self.__import__('pkg.fake')
-                module = self.__import__('', globals= globals_,
-                                                fromlist=['attr'], level=2)
-            self.assertEqual(module.__name__, 'pkg')
+        module = self.import_module({'__name__': 'pkg.fake', '__path__': []})
+        self.assertEqual(module.__name__, 'pkg')
+
+    def test_warn_when_using___name__(self):
+        with self.assertWarns(ImportWarning):
+            self.import_module({'__name__': 'pkg.fake', '__path__': []})
 
     def test_None_as___package__(self):
         # [None]
-        self.test_using___name__(package_as_None=True)
+        module = self.import_module({
+            '__name__': 'pkg.fake', '__path__': [], '__package__': None })
+        self.assertEqual(module.__name__, 'pkg')
+
+    def test_prefers___spec__(self):
+        globals = {'__spec__': FakeSpec()}
+        with self.assertRaises(SystemError):
+            self.__import__('', globals, {}, ['relimport'], 1)
 
     def test_bad__package__(self):
         globals = {'__package__': '<not real>'}
@@ -70,6 +78,10 @@ class Using__package__:
             self.__import__('', globals, {}, ['relimport'], 1)
 
 
+class FakeSpec:
+    parent = '<fake>'
+
+
 class Using__package__PEP302(Using__package__):
     mock_modules = util.mock_modules