Backported issue #4589 to Python 2.5.3: Propagated an exception thrown by a

context manager's __exit__ method's result while it's being converted to bool.

diff --git a/Lib/test/test_with.py b/Lib/test/test_with.py
index 3ba897798bf7065c5785080d19209931a03c00c5..3004675414d6c55fec2c9148e0ee2e52da669c2e 100644 (file)
--- a/Lib/test/test_with.py
+++ b/Lib/test/test_with.py
@@ -505,6 +505,36 @@ class ExceptionalTestCase(unittest.TestCase, ContextmanagerAssertionMixin):
 
         self.assertRaises(GeneratorExit, shouldThrow)
 
+    def testErrorsInBool(self):
+        # issue4589: __exit__ return code may raise an exception
+        # when looking at its truth value.
+
+        class cm(object):
+            def __init__(self, bool_conversion):
+                class Bool:
+                    def __nonzero__(self):
+                        return bool_conversion()
+                self.exit_result = Bool()
+            def __enter__(self):
+                return 3
+            def __exit__(self, a, b, c):
+                return self.exit_result
+
+        def trueAsBool():
+            with cm(lambda: True):
+                self.fail("Should NOT see this")
+        trueAsBool()
+
+        def falseAsBool():
+            with cm(lambda: False):
+                self.fail("Should raise")
+        self.assertRaises(AssertionError, falseAsBool)
+
+        def failAsBool():
+            with cm(lambda: 1//0):
+                self.fail("Should NOT see this")
+        self.assertRaises(ZeroDivisionError, failAsBool)
+
 
 class NonLocalFlowControlTestCase(unittest.TestCase):
 

diff --git a/Misc/NEWS b/Misc/NEWS
index eee00850662517eb58967bacea95a17e3277c075..60a4c67de7ab81500a6bde44097e5548e2837836 100644 (file)
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@ What's New in Python 2.5.3?
 Core and builtins
 -----------------
 
+- Issue #4589: Propagated an exception thrown by a context manager's
+  __exit__ method's result while it's being converted to bool.
+
 - Issue #4317: Fixed a crash in the imageop.rgb2rgb8() function.
 
 - Issue #4230: If ``__getattr__`` is a descriptor, it now functions correctly.

diff --git a/Python/ceval.c b/Python/ceval.c
index ddfe3c48eadd9b31bc8f30b74a137c81fe42c81e..d74149c4a936710fab3f8289b36c36ec669e2923 100644 (file)
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -2263,9 +2263,16 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
                        x = PyObject_CallFunctionObjArgs(x, u, v, w, NULL);
                        if (x == NULL)
                                break; /* Go to error exit */
-                       if (u != Py_None && PyObject_IsTrue(x)) {
+                       if (u != Py_None)
+                               err = PyObject_IsTrue(x);
+                       else
+                               err = 0;
+                       Py_DECREF(x);
+                       if (err < 0)
+                               break; /* Go to error exit */
+                       else if (err > 0) {
+                               err = 0;
                                /* There was an exception and a true return */
-                               Py_DECREF(x);
                                x = TOP(); /* Again */
                                STACKADJ(-3);
                                Py_INCREF(Py_None);
@@ -2276,7 +2283,6 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
                                Py_DECREF(w);
                        } else {
                                /* Let END_FINALLY do its thing */
-                               Py_DECREF(x);
                                x = POP();
                                Py_DECREF(x);
                        }