importlib.__import__() now raises ValueError when level < 0.

This is to bring it more in line with what PEP 328 set out to do with
removing ambiguous absolute/relative import semantics.

Lib/importlib/_bootstrap.py

@@ -1048,6 +1048,8 @@ def __import__(name, globals={}, locals={}, fromlist=[], level=0):
         raise TypeError("module name must be str, not {}".format(type(name)))
     if level == 0:
         module = _gcd_import(name)
+    elif level < 0:
+        raise ValueError('level must be >= 0')
     else:
         package = _calc___package__(globals)
         module = _gcd_import(name, package, level)

Lib/importlib/test/import_/test_api.py

@@ -12,6 +12,13 @@ class APITest(unittest.TestCase):
         with self.assertRaises(TypeError):
             util.import_(42)
 
+    def test_negative_level(self):
+        # Raise ValueError when a negative level is specified.
+        # PEP 328 did away with sys.module None entries and the ambiguity of
+        # absolute/relative imports.
+        with self.assertRaises(ValueError):
+            util.import_('os', globals(), level=-1)
+
 
 def test_main():
     from test.support import run_unittest

Misc/NEWS

@@ -466,6 +466,9 @@ Core and Builtins
 Library
 -------
 
+- Do away with ambiguous level values (as suggested by PEP 328) in
+  importlib.__import__() by raising ValueError when level < 0.
+
 - Issue #2489: pty.spawn could consume 100% cpu when it encountered an EOF.
 
 - Issue #13014: Fix a possible reference leak in SSLSocket.getpeercert().