Issue #26367: Have importlib.__init__() raise RuntimeError when

'level' is specified but no __package__.

This brings the function inline with builtins.__import__(). Thanks to
Manuel Jacob for the patch.

Lib/importlib/_bootstrap.py

@@ -922,7 +922,7 @@ def _sanity_check(name, package, level):
         raise TypeError('module name must be str, not {}'.format(type(name)))
     if level < 0:
         raise ValueError('level must be >= 0')
-    if package:
+    if level > 0:
         if not isinstance(package, str):
             raise TypeError('__package__ not set to a string')
         elif package not in sys.modules:

Lib/test/test_importlib/import_/test_relative_imports.py

@@ -207,6 +207,11 @@ class RelativeImports:
         with self.assertRaises(KeyError):
             self.__import__('sys', level=1)
 
+    def test_relative_import_no_package_exists_absolute(self):
+        with self.assertRaises(SystemError):
+            self.__import__('sys', {'__package__': '', '__spec__': None},
+                            level=1)
+
 
 (Frozen_RelativeImports,
  Source_RelativeImports