#4559: When a context manager's __exit__() method returns an object whose

conversion to bool raises an exception, 'with' loses that exception.

Reviewed by Jeffrey Yasskin.
Already ported to 2.5, will port to 2.6 and 3.0

diff --git a/Lib/test/test_with.py b/Lib/test/test_with.py
index 3007e5aa2c7a3e99469fe41b89d6c567667916e0..bfeb06bdd9baa539c07e0ed4be6e1f18831bdb4b 100644 (file)
--- a/Lib/test/test_with.py
+++ b/Lib/test/test_with.py
@@ -503,6 +503,36 @@ 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 8a86d7c72e9b9d7859240d1ef32744af8ebf987b..e964ced76bc5ca3cc7c1cf264e797555d30cadd9 100644 (file)
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@ What's New in Python 2.7 alpha 1
 Core and Builtins
 -----------------
 
+- Issue #4597: Fixed exception handling when the __exit__ function of a
+  context manager returns a value that cannot be converted to a bool.
+
 - Issue #4597: Fixed several opcodes that weren't always propagating
   exceptions.
 

diff --git a/Python/ceval.c b/Python/ceval.c
index 0a1d86a9d702f3f7ba0cb7520e94ac9d2a02d4e7..bd35185c8464ccf1149c3ce4e464817a57ef0a70 100644 (file)
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -2349,11 +2349,20 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
                        /* XXX Not the fastest way to call it... */
                        x = PyObject_CallFunctionObjArgs(exit_func, u, v, w,
                                                         NULL);
-                       if (x == NULL) {
-                               Py_DECREF(exit_func);
+                       Py_DECREF(exit_func);
+                       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 */
                                STACKADJ(-2);
                                Py_INCREF(Py_None);
@@ -2365,8 +2374,6 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
                                /* The stack was rearranged to remove EXIT
                                   above. Let END_FINALLY do its thing */
                        }
-                       Py_DECREF(x);
-                       Py_DECREF(exit_func);
                        PREDICT(END_FINALLY);
                        break;
                }