Implicit exception chaining via __context__ (PEP 3134).

Patch 3108 by Antooine Pitrou.

2 files changed, 102 insertions, 27 deletions

diff --git a/Lib/test/test_exceptions.py b/Lib/test/test_exceptions.py
index 9068554..55a57ba 100644
--- a/Lib/test/test_exceptions.py
+++ b/Lib/test/test_exceptions.py
@@ -480,7 +480,12 @@ class ExceptionTests(unittest.TestCase):
                 inner_raising_func()
             except:
                 raise KeyError
-        except KeyError:
+        except KeyError as e:
+            # We want to test that the except block above got rid of
+            # the exception raised in inner_raising_func(), but it
+            # also ends up in the __context__ of the KeyError, so we
+            # must clear the latter manually for our test to succeed.
+            e.__context__ = None
             obj = None
             obj = wr()
             self.failUnless(obj is None, "%s" % obj)
diff --git a/Lib/test/test_raise.py b/Lib/test/test_raise.py
index 5f0070e..3072c14 100644
--- a/Lib/test/test_raise.py
+++ b/Lib/test/test_raise.py
@@ -181,32 +181,102 @@ class TestTraceback(unittest.TestCase):
             self.fail("No exception raised")
 
 
-# Disabled until context is implemented
-# class TestContext(object):
-#     def test_instance_context_bare_raise(self):
-#         context = IndexError()
-#         try:
-#             try:
-#                 raise context
-#             except:
-#                 raise OSError()
-#         except OSError as e:
-#             self.assertEqual(e.__context__, context)
-#         else:
-#             self.fail("No exception raised")
-#
-#     def test_class_context_bare_raise(self):
-#         context = IndexError
-#         try:
-#             try:
-#                 raise context
-#             except:
-#                 raise OSError()
-#         except OSError as e:
-#             self.assertNotEqual(e.__context__, context)
-#             self.failUnless(isinstance(e.__context__, context))
-#         else:
-#             self.fail("No exception raised")
+class TestContext(unittest.TestCase):
+    def test_instance_context_instance_raise(self):
+        context = IndexError()
+        try:
+            try:
+                raise context
+            except:
+                raise OSError()
+        except OSError as e:
+            self.assertEqual(e.__context__, context)
+        else:
+            self.fail("No exception raised")
+
+    def test_class_context_instance_raise(self):
+        context = IndexError
+        try:
+            try:
+                raise context
+            except:
+                raise OSError()
+        except OSError as e:
+            self.assertNotEqual(e.__context__, context)
+            self.failUnless(isinstance(e.__context__, context))
+        else:
+            self.fail("No exception raised")
+
+    def test_class_context_class_raise(self):
+        context = IndexError
+        try:
+            try:
+                raise context
+            except:
+                raise OSError
+        except OSError as e:
+            self.assertNotEqual(e.__context__, context)
+            self.failUnless(isinstance(e.__context__, context))
+        else:
+            self.fail("No exception raised")
+
+    def test_c_exception_context(self):
+        try:
+            try:
+                1/0
+            except:
+                raise OSError
+        except OSError as e:
+            self.failUnless(isinstance(e.__context__, ZeroDivisionError))
+        else:
+            self.fail("No exception raised")
+
+    def test_c_exception_raise(self):
+        try:
+            try:
+                1/0
+            except:
+                xyzzy
+        except NameError as e:
+            self.failUnless(isinstance(e.__context__, ZeroDivisionError))
+        else:
+            self.fail("No exception raised")
+
+    def test_noraise_finally(self):
+        try:
+            try:
+                pass
+            finally:
+                raise OSError
+        except OSError as e:
+            self.failUnless(e.__context__ is None)
+        else:
+            self.fail("No exception raised")
+
+    def test_raise_finally(self):
+        try:
+            try:
+                1/0
+            finally:
+                raise OSError
+        except OSError as e:
+            self.failUnless(isinstance(e.__context__, ZeroDivisionError))
+        else:
+            self.fail("No exception raised")
+
+    def test_context_manager(self):
+        class ContextManager:
+            def __enter__(self):
+                pass
+            def __exit__(self, t, v, tb):
+                xyzzy
+        try:
+            with ContextManager():
+                1/0
+        except NameError as e:
+            self.failUnless(isinstance(e.__context__, ZeroDivisionError))
+        else:
+            self.fail("No exception raised")
 
 
 class TestRemovedFunctionality(unittest.TestCase):