gh-96348: Deprecate the 3-arg signature of coroutine.throw, generator.throw and agen.athrow

Lib/contextlib.py

@@ -152,7 +152,7 @@ def __exit__(self, typ, value, traceback):
                 # tell if we get the same exception back
                 value = typ()
             try:
-                self.gen.throw(typ, value, traceback)
+                self.gen.throw(value)
             except StopIteration as exc:
                 # Suppress StopIteration *unless* it's the same exception that
                 # was passed to throw().  This prevents a StopIteration
@@ -219,7 +219,7 @@ async def __aexit__(self, typ, value, traceback):
                 # tell if we get the same exception back
                 value = typ()
             try:
-                await self.gen.athrow(typ, value, traceback)
+                await self.gen.athrow(value)
             except StopAsyncIteration as exc:
                 # Suppress StopIteration *unless* it's the same exception that
                 # was passed to throw().  This prevents a StopIteration

Lib/test/test_asyncgen.py

@@ -650,7 +650,7 @@ def test1(anext):
             agen = agenfn()
             with contextlib.closing(anext(agen, "default").__await__()) as g:
                 self.assertEqual(g.send(None), 1)
-                self.assertEqual(g.throw(MyError, MyError(), None), 2)
+                self.assertEqual(g.throw(MyError()), 2)
                 try:
                     g.send(None)
                 except StopIteration as e:
@@ -663,9 +663,9 @@ def test2(anext):
             agen = agenfn()
             with contextlib.closing(anext(agen, "default").__await__()) as g:
                 self.assertEqual(g.send(None), 1)
-                self.assertEqual(g.throw(MyError, MyError(), None), 2)
+                self.assertEqual(g.throw(MyError()), 2)
                 with self.assertRaises(MyError):
-                    g.throw(MyError, MyError(), None)
+                    g.throw(MyError())
 
         def test3(anext):
             agen = agenfn()
@@ -692,9 +692,9 @@ async def agenfn():
             agen = agenfn()
             with contextlib.closing(anext(agen, "default").__await__()) as g:
                 self.assertEqual(g.send(None), 10)
-                self.assertEqual(g.throw(MyError, MyError(), None), 20)
+                self.assertEqual(g.throw(MyError()), 20)
                 with self.assertRaisesRegex(MyError, 'val'):
-                    g.throw(MyError, MyError('val'), None)
+                    g.throw(MyError('val'))
 
         def test5(anext):
             @types.coroutine
@@ -713,7 +713,7 @@ async def agenfn():
             with contextlib.closing(anext(agen, "default").__await__()) as g:
                 self.assertEqual(g.send(None), 10)
                 with self.assertRaisesRegex(StopIteration, 'default'):
-                    g.throw(MyError, MyError(), None)
+                    g.throw(MyError())
 
         def test6(anext):
             @types.coroutine
@@ -728,7 +728,7 @@ async def agenfn():
             agen = agenfn()
             with contextlib.closing(anext(agen, "default").__await__()) as g:
                 with self.assertRaises(MyError):
-                    g.throw(MyError, MyError(), None)
+                    g.throw(MyError())
 
         def run_test(test):
             with self.subTest('pure-Python anext()'):

Lib/test/test_asyncio/test_futures.py

@@ -10,6 +10,7 @@
 from types import GenericAlias
 import asyncio
 from asyncio import futures
+import warnings
 from test.test_asyncio import utils as test_utils
 from test import support
 
@@ -619,10 +620,12 @@ def test_future_stop_iteration_args(self):
     def test_future_iter_throw(self):
         fut = self._new_future(loop=self.loop)
         fi = iter(fut)
-        self.assertRaises(TypeError, fi.throw,
-                          Exception, Exception("elephant"), 32)
-        self.assertRaises(TypeError, fi.throw,
-                          Exception("elephant"), Exception("elephant"))
+        with warnings.catch_warnings():
+            warnings.filterwarnings("ignore", category=DeprecationWarning)
+            self.assertRaises(TypeError, fi.throw,
+                            Exception, Exception("elephant"), 32)
+            self.assertRaises(TypeError, fi.throw,
+                            Exception("elephant"), Exception("elephant"))
         self.assertRaises(TypeError, fi.throw, list)
 
     def test_future_del_collect(self):

Lib/test/test_coroutines.py

@@ -709,7 +709,7 @@ async def foo():
         aw = coro.__await__()
         next(aw)
         with self.assertRaises(ZeroDivisionError):
-            aw.throw(ZeroDivisionError, None, None)
+            aw.throw(ZeroDivisionError())
         self.assertEqual(N, 102)
 
     def test_func_11(self):

Lib/test/test_generators.py

@@ -2113,6 +2113,13 @@ def printsolution(self, x):
 >>> g.throw(ValueError("xyz"))  # value only
 caught ValueError (xyz)
 
+>>> import warnings
+>>> warnings.filterwarnings("ignore", category=DeprecationWarning)
+
+# Filter DeprecationWarning: the (type, val, tb) exception representation is deprecated,
+#                            and may be removed in a future version of Python.
+# Will re-enable it soon.
+
 >>> g.throw(ValueError, ValueError(1))   # value+matching type
 caught ValueError (1)
 
@@ -2181,6 +2188,12 @@ def printsolution(self, x):
   ...
 ValueError: 7
 
+>>> warnings.filters.pop(0)
+('ignore', None, <class 'DeprecationWarning'>, None, 0)
+
+# Re-enable DeprecationWarning: the (type, val, tb) exception representation is deprecated,
+#                               and may be removed in a future version of Python.
+
 Plain "raise" inside a generator should preserve the traceback (#13188).
 The traceback should have 3 levels:
 - g.throw()

Lib/test/test_types.py

@@ -2072,7 +2072,7 @@ def foo(): return gen
         wrapper = foo()
         wrapper.send(None)
         with self.assertRaisesRegex(Exception, 'ham'):
-            wrapper.throw(Exception, Exception('ham'))
+            wrapper.throw(Exception('ham'))
 
         # decorate foo second time
         foo = types.coroutine(foo)

Misc/NEWS.d/next/Core and Builtins/2022-08-31-18-46-13.gh-issue-96348.xzCoTP.rst

@@ -0,0 +1 @@
+Emit a DeprecationWarning when :meth:`~generator.throw` or :meth:`~coroutine.throw` are called with more than one argument.

Objects/genobject.c

@@ -418,7 +418,9 @@ PyDoc_STRVAR(throw_doc,
 throw(type[,value[,tb]])\n\
 \n\
 Raise exception in generator, return next yielded value or raise\n\
-StopIteration.");
+StopIteration.\n\
+the (type, val, tb) exception representation is deprecated, \n\
+and may be removed in a future version of Python.");
 
 static PyObject *
 _gen_throw(PyGenObject *gen, int close_on_genexit,
@@ -559,6 +561,14 @@ gen_throw(PyGenObject *gen, PyObject *const *args, Py_ssize_t nargs)
     if (!_PyArg_CheckPositional("throw", nargs, 1, 3)) {
         return NULL;
     }
+    if (nargs > 1) {
+        if (PyErr_WarnEx(PyExc_DeprecationWarning,
+                            "the (type, val, tb) exception representation is deprecated, "
+                            "and may be removed in a future version of Python.",
+                            1) < 0) {
+            return NULL;
+        }
+    }
     typ = args[0];
     if (nargs == 3) {
         val = args[1];
@@ -1147,7 +1157,10 @@ PyDoc_STRVAR(coro_throw_doc,
 throw(type[,value[,traceback]])\n\
 \n\
 Raise exception in coroutine, return next iterated value or raise\n\
-StopIteration.");
+StopIteration.\n\
+the (type, val, tb) exception representation is deprecated, \n\
+and may be removed in a future version of Python.");
+
 
 PyDoc_STRVAR(coro_close_doc,
 "close() -> raise GeneratorExit inside coroutine.");