bpo-21720: Restore the Python 2.7 logic in handling a fromlist. (#4118)

BytesWarning no longer emitted when the fromlist argument of
__import__() or the __all__ attribute of the module contain bytes
instances.

Lib/importlib/_bootstrap.py

@@ -994,7 +994,7 @@ def _gcd_import(name, package=None, level=0):
     return _find_and_load(name, _gcd_import)
 
 
-def _handle_fromlist(module, fromlist, import_):
+def _handle_fromlist(module, fromlist, import_, *, recursive=False):
     """Figure out what __import__ should return.
 
     The import_ parameter is a callable which takes the name of module to
@@ -1005,13 +1005,19 @@ def _handle_fromlist(module, fromlist, import_):
     # The hell that is fromlist ...
     # If a package was imported, try to import stuff from fromlist.
     if hasattr(module, '__path__'):
-        if '*' in fromlist:
-            fromlist = list(fromlist)
-            fromlist.remove('*')
-            if hasattr(module, '__all__'):
-                fromlist.extend(module.__all__)
         for x in fromlist:
-            if not hasattr(module, x):
+            if not isinstance(x, str):
+                if recursive:
+                    where = module.__name__ + '.__all__'
+                else:
+                    where = "``from list''"
+                raise TypeError(f"Item in {where} must be str, "
+                                f"not {type(x).__name__}")
+            elif x == '*':
+                if not recursive and hasattr(module, '__all__'):
+                    _handle_fromlist(module, module.__all__, import_,
+                                     recursive=True)
+            elif not hasattr(module, x):
                 from_name = '{}.{}'.format(module.__name__, x)
                 try:
                     _call_with_frames_removed(import_, from_name)

Lib/test/test_importlib/import_/test_fromlist.py

@@ -1,5 +1,6 @@
 """Test that the semantics relating to the 'fromlist' argument are correct."""
 from .. import util
+import warnings
 import unittest
 
 
@@ -73,6 +74,13 @@ class HandlingFromlist:
                 self.assertTrue(hasattr(module, 'module'))
                 self.assertEqual(module.module.__name__, 'pkg.module')
 
+    def test_nonexistent_from_package(self):
+        with util.mock_modules('pkg.__init__') as importer:
+            with util.import_state(meta_path=[importer]):
+                module = self.__import__('pkg', fromlist=['non_existent'])
+                self.assertEqual(module.__name__, 'pkg')
+                self.assertFalse(hasattr(module, 'non_existent'))
+
     def test_module_from_package_triggers_ModuleNotFoundError(self):
         # If a submodule causes an ModuleNotFoundError because it tries
         # to import a module which doesn't exist, that should let the
@@ -122,6 +130,41 @@ class HandlingFromlist:
                 self.assertEqual(module.module1.__name__, 'pkg.module1')
                 self.assertEqual(module.module2.__name__, 'pkg.module2')
 
+    def test_nonexistent_in_all(self):
+        with util.mock_modules('pkg.__init__') as importer:
+            with util.import_state(meta_path=[importer]):
+                importer['pkg'].__all__ = ['non_existent']
+                module = self.__import__('pkg', fromlist=['*'])
+                self.assertEqual(module.__name__, 'pkg')
+                self.assertFalse(hasattr(module, 'non_existent'))
+
+    def test_star_in_all(self):
+        with util.mock_modules('pkg.__init__') as importer:
+            with util.import_state(meta_path=[importer]):
+                importer['pkg'].__all__ = ['*']
+                module = self.__import__('pkg', fromlist=['*'])
+                self.assertEqual(module.__name__, 'pkg')
+                self.assertFalse(hasattr(module, '*'))
+
+    def test_invalid_type(self):
+        with util.mock_modules('pkg.__init__') as importer:
+            with util.import_state(meta_path=[importer]), \
+                 warnings.catch_warnings():
+                warnings.simplefilter('error', BytesWarning)
+                with self.assertRaisesRegex(TypeError, r'\bfrom\b'):
+                    self.__import__('pkg', fromlist=[b'attr'])
+                with self.assertRaisesRegex(TypeError, r'\bfrom\b'):
+                    self.__import__('pkg', fromlist=iter([b'attr']))
+
+    def test_invalid_type_in_all(self):
+        with util.mock_modules('pkg.__init__') as importer:
+            with util.import_state(meta_path=[importer]), \
+                 warnings.catch_warnings():
+                warnings.simplefilter('error', BytesWarning)
+                importer['pkg'].__all__ = [b'attr']
+                with self.assertRaisesRegex(TypeError, r'\bpkg\.__all__\b'):
+                    self.__import__('pkg', fromlist=['*'])
+
 
 (Frozen_FromList,
  Source_FromList

Misc/NEWS.d/next/Core and Builtins/2017-10-25-15-51-37.bpo-21720.BwIKLP.rst

@@ -0,0 +1,3 @@
+BytesWarning no longer emitted when the *fromlist* argument of
+``__import__()`` or the ``__all__`` attribute of the module contain bytes
+instances.