Implement sys._set_exception() instead of using ctypes

Author: pR0Ps

Lib/contextlib.py

@@ -15,14 +15,6 @@
            "chdir"]
 
 
-_PyErr_SetHandledException = ctypes.pythonapi.PyErr_SetHandledException
-_PyErr_SetHandledException.argtypes = [ctypes.py_object]
-def _set_current_exception(exc):
-    if exc is not None and not isinstance(exc, BaseException):
-        raise TypeError(f"{exc!r} is not an exception")
-    _PyErr_SetHandledException(exc)
-
-
 class AbstractContextManager(abc.ABC):
 
     """An abstract base class for context managers."""
@@ -178,7 +170,7 @@ def __exit__(self, typ, value, traceback):
                 # context here. In order to make the context manager behave
                 # like a normal function we set the current exception context
                 # to what it was during the context manager's __enter__
-                _set_current_exception(exc_context)
+                sys._set_exception(exc_context)
                 self.gen.throw(value)
             except StopIteration as exc:
                 # Suppress StopIteration *unless* it's the same exception that

Lib/test/test_sys.py

@@ -142,6 +142,71 @@ def f():
         self.assertIsInstance(e, ValueError)
         self.assertIs(exc, e)
 
+class SetExceptionTests(unittest.TestCase):
+
+    def tearDown(self):
+        # make sure we don't leave the global exception set
+        sys._set_exception(None);
+
+    def test_set_exc_invalid_values(self):
+        for x in (0, "1", b"2"):
+            with self.assertRaises(TypeError):
+                sys._set_exception(x);
+
+    def test_clear_exc(self):
+        try:
+            raise ValueError()
+        except ValueError:
+            self.assertIsInstance(sys.exception(), ValueError)
+            sys._set_exception(None)
+            self.assertIsNone(sys.exception())
+
+    def test_set_exc(self):
+        exc = ValueError()
+        self.assertIsNone(sys.exception())
+        sys._set_exception(exc)
+        self.assertIs(sys.exception(), exc)
+
+    def test_set_exc_replaced_by_new_exception_and_restored(self):
+        exc = ValueError()
+        sys._set_exception(exc)
+        self.assertIs(sys.exception(), exc)
+        try:
+            raise TypeError()
+        except TypeError:
+            self.assertIsInstance(sys.exception(), TypeError)
+            self.assertIs(sys.exception().__context__, exc)
+
+        self.assertIs(sys.exception(), exc)
+
+    def test_set_exc_popped_on_exit_except(self):
+        exc = ValueError()
+        try:
+            raise TypeError()
+        except TypeError:
+            self.assertIsInstance(sys.exception(), TypeError)
+            sys._set_exception(exc)
+            self.assertIs(sys.exception(), exc)
+        self.assertIsNone(sys.exception())
+
+    def test_cleared_exc_overridden_and_restored(self):
+        try:
+            raise ValueError()
+        except ValueError:
+            try:
+                raise TypeError()
+            except TypeError:
+                self.assertIsInstance(sys.exception(), TypeError)
+                sys._set_exception(None)
+                self.assertIsNone(sys.exception())
+                try:
+                    raise IndexError()
+                except IndexError:
+                    self.assertIsInstance(sys.exception(), IndexError)
+                    self.assertIsNone(sys.exception().__context__)
+                self.assertIsNone(sys.exception())
+            self.assertIsInstance(sys.exception(), ValueError)
+        self.assertIsNone(sys.exception())
 
 class ExceptHookTest(unittest.TestCase):
 

Python/clinic/sysmodule.c.h

@@ -824,6 +824,32 @@ sys_exception_impl(PyObject *module)
     Py_RETURN_NONE;
 }
 
+/*[clinic input]
+sys._set_exception
+    exception: object
+
+Set the current exception.
+
+Subsequent calls to sys.exception()/sys.exc_info() will return
+the provided exception until another exception is raised in the
+current thread or the execution stack returns to a frame where
+another exception is being handled.
+[clinic start generated code]*/
+
+static PyObject *
+sys__set_exception_impl(PyObject *module, PyObject *exception)
+/*[clinic end generated code: output=39e119ee6b747085 input=46da3b45313a1cfa]*/
+{
+    if (!Py_IsNone(exception) && !PyExceptionInstance_Check(exception)){
+        PyErr_SetString(
+            PyExc_TypeError,
+            "must be an exception/None"
+        );
+        return NULL;
+    }
+    PyErr_SetHandledException(exception);
+    Py_RETURN_NONE;
+}
 
 /*[clinic input]
 sys.exc_info
@@ -2400,6 +2426,7 @@ static PyMethodDef sys_methods[] = {
     SYS__CURRENT_EXCEPTIONS_METHODDEF
     SYS_DISPLAYHOOK_METHODDEF
     SYS_EXCEPTION_METHODDEF
+    SYS__SET_EXCEPTION_METHODDEF
     SYS_EXC_INFO_METHODDEF
     SYS_EXCEPTHOOK_METHODDEF
     SYS_EXIT_METHODDEF