Issue #15316: Let exceptions raised during imports triggered by the

brettcannon · brettcannon · commit 12c6bda4f0e9 · 2012-08-24T18:25:59.000-04:00
fromlist of __import__ propagate.

The problem previously was that if something listed in fromlist didn't
exist then that's okay. The fix for that was too broad in terms of
catching ImportError.

The trick with the solution to this issue is that the proper
refactoring of import thanks to importlib doesn't allow for a way to
distinguish (portably) between an ImportError because finders couldn't
find a loader, or a loader raised the exception. In Python 3.4 the
hope is to introduce a new exception (e.g. ModuleNotFound) to make it
clean to differentiate why ImportError was raised.
diff --git a/Lib/importlib/_bootstrap.py b/Lib/importlib/_bootstrap.py
@@ -1513,7 +1513,11 @@ def _find_and_load_unlocked(name, import_):
             raise ImportError(msg, name=name)
     loader = _find_module(name, path)
     if loader is None:
-        raise ImportError(_ERR_MSG.format(name), name=name)
+        exc = ImportError(_ERR_MSG.format(name), name=name)
+        # TODO(brett): switch to a proper ModuleNotFound exception in Python
+        # 3.4.
+        exc._not_found = True
+        raise exc
     elif name not in sys.modules:
         # The parent import may have already imported this module.
         loader.load_module(name)
@@ -1599,10 +1603,16 @@ def _handle_fromlist(module, fromlist, import_):
                 try:
                     _call_with_frames_removed(import_,
                                       '{}.{}'.format(module.__name__, x))
-                except ImportError:
+                except ImportError as exc:
                     # Backwards-compatibility dictates we ignore failed
-                    # imports triggered by fromlist.
-                    pass
+                    # imports triggered by fromlist for modules that don't
+                    # exist.
+                    # TODO(brett): In Python 3.4, have import raise
+                    #   ModuleNotFound and catch that.
+                    if hasattr(exc, '_not_found') and exc._not_found:
+                        pass
+                    else:
+                        raise
     return module
 
 
diff --git a/Lib/test/test_importlib/import_/test_api.py b/Lib/test/test_importlib/import_/test_api.py
@@ -1,7 +1,22 @@
+from .. import util as importlib_test_util
 from . import util
+import imp
+import sys
 import unittest
 
 
+class BadLoaderFinder:
+    bad = 'fine.bogus'
+    @classmethod
+    def find_module(cls, fullname, path):
+        if fullname == cls.bad:
+            return cls
+    @classmethod
+    def load_module(cls, fullname):
+        if fullname == cls.bad:
+            raise ImportError('I cannot be loaded!')
+
+
 class APITest(unittest.TestCase):
 
     """Test API-specific details for __import__ (e.g. raising the right
@@ -19,6 +34,29 @@ def test_negative_level(self):
         with self.assertRaises(ValueError):
             util.import_('os', globals(), level=-1)
 
+    def test_nonexistent_fromlist_entry(self):
+        # If something in fromlist doesn't exist, that's okay.
+        # issue15715
+        mod = imp.new_module('fine')
+        mod.__path__ = ['XXX']
+        with importlib_test_util.import_state(meta_path=[BadLoaderFinder]):
+            with importlib_test_util.uncache('fine'):
+                sys.modules['fine'] = mod
+                util.import_('fine', fromlist=['not here'])
+
+    def test_fromlist_load_error_propagates(self):
+        # If something in fromlist triggers an exception not related to not
+        # existing, let that exception propagate.
+        # issue15316
+        mod = imp.new_module('fine')
+        mod.__path__ = ['XXX']
+        with importlib_test_util.import_state(meta_path=[BadLoaderFinder]):
+            with importlib_test_util.uncache('fine'):
+                sys.modules['fine'] = mod
+                with self.assertRaises(ImportError):
+                    util.import_('fine', fromlist=['bogus'])
+
+
 
 def test_main():
     from test.support import run_unittest
diff --git a/Misc/NEWS b/Misc/NEWS
@@ -10,6 +10,10 @@ What's New in Python 3.3.0 Release Candidate 1?
 Core and Builtins
 -----------------
 
+- Issue #15316: When an item in the fromlist for __import__ doesn't exist,
+  don't raise an error, but if an exception is raised as part of an import do
+  let that propagate.
+
 - Issue #15778: ensure that str(ImportError(msg)) returns a str
   even when msg isn't a str.
 
diff --git a/Python/importlib.h b/Python/importlib.h
