From 565d78586babda2b62cbe4f89c2dd3cace79c0fa Mon Sep 17 00:00:00 2001
From: Benjamin Peterson <benjamin@python.org>
Date: Fri, 5 Feb 2010 02:12:14 +0000
Subject: normalize exceptions passed to the __exit__ method #7853

In Python 2.x, exceptions in finally blocks are not normalized.  Since with
statements are implemented using finally blocks, ceval.c had to be tweaked to
distinguish between with finally blocks and normal ones.

A test for the finalization of generators containing with statements was also
added.
---
 Lib/test/test_generators.py | 11 +++++++++++
 Lib/test/test_with.py       |  1 -
 Misc/NEWS                   |  3 +++
 Python/ceval.c              | 14 +++++++++-----
 Python/compile.c            |  3 +++
 5 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/Lib/test/test_generators.py b/Lib/test/test_generators.py
index ad7e17c..19bfe07 100644
--- a/Lib/test/test_generators.py
+++ b/Lib/test/test_generators.py
@@ -1700,6 +1700,17 @@ And finalization:
 >>> del g
 exiting
 
+>>> class context(object):
+...    def __enter__(self): pass
+...    def __exit__(self, *args): print 'exiting'
+>>> def f():
+...     with context():
+...          yield
+>>> g = f()
+>>> g.next()
+>>> del g
+exiting
+
 
 GeneratorExit is not caught by except Exception:
 
diff --git a/Lib/test/test_with.py b/Lib/test/test_with.py
index 4b947d8..a1ec80b 100644
--- a/Lib/test/test_with.py
+++ b/Lib/test/test_with.py
@@ -361,7 +361,6 @@ class ExceptionalTestCase(unittest.TestCase, ContextmanagerAssertionMixin):
         self.assertAfterWithManagerInvariantsWithError(cm)
         self.assertAfterWithGeneratorInvariantsWithError(self.resource)
 
-    @unittest.expectedFailure
     def testExceptionNormalized(self):
         cm = mock_contextmanager_generator()
         def shouldThrow():
diff --git a/Misc/NEWS b/Misc/NEWS
index 6bb355b..9225c6f 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@ What's New in Python 2.7 alpha 3?
 Core and Builtins
 -----------------
 
+- Issue #7853: Normalize exceptions before they are passed to a context managers
+  __exit__ method.
+
 - Issue #7385: Fix a crash in `MemoryView_FromObject` when
   `PyObject_GetBuffer` fails.  Patch by Florent Xicluna.
 
diff --git a/Python/ceval.c b/Python/ceval.c
index d501a4e..0b8a377 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -2555,9 +2555,11 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
 			Py_DECREF(u);
 			if (!x)
 				break;
-			/* Setup the finally block before pushing the result
-			   of __enter__ on the stack. */
-			PyFrame_BlockSetup(f, SETUP_FINALLY, INSTR_OFFSET() + oparg,
+			/* Setup a finally block (SETUP_WITH as a block is
+			   equivalent to SETUP_FINALLY except it normalizes
+			   the exception) before pushing the result of
+			   __enter__ on the stack. */
+			PyFrame_BlockSetup(f, SETUP_WITH, INSTR_OFFSET() + oparg,
 					   STACK_LEVEL());
 
 			PUSH(x);
@@ -2898,7 +2900,8 @@ fast_block_end:
 			}
 			if (b->b_type == SETUP_FINALLY ||
 			    (b->b_type == SETUP_EXCEPT &&
-			     why == WHY_EXCEPTION)) {
+			     why == WHY_EXCEPTION) ||
+			    b->b_type == SETUP_WITH) {
 				if (why == WHY_EXCEPTION) {
 					PyObject *exc, *val, *tb;
 					PyErr_Fetch(&exc, &val, &tb);
@@ -2911,7 +2914,8 @@ fast_block_end:
 					   so a program can emulate the
 					   Python main loop.  Don't do
 					   this for 'finally'. */
-					if (b->b_type == SETUP_EXCEPT) {
+					if (b->b_type == SETUP_EXCEPT ||
+					    b->b_type == SETUP_WITH) {
 						PyErr_NormalizeException(
 							&exc, &val, &tb);
 						set_exc_info(tstate,
diff --git a/Python/compile.c b/Python/compile.c
index 1e27539..4ea2ee9 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -2927,6 +2927,9 @@ compiler_with(struct compiler *c, stmt_ty s)
 
     /* SETUP_WITH pushes a finally block. */
     compiler_use_next_block(c, block);
+    /* Note that the block is actually called SETUP_WITH in ceval.c, but
+       functions the same as SETUP_FINALLY except that exceptions are
+       normalized. */
     if (!compiler_push_fblock(c, FINALLY_TRY, block)) {
 	return 0;
     }
-- 
cgit v0.12