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Issue #23353: Fix the exception handling of generators in PyEval_EvalFrameEx().
At entry, save or swap the exception state even if PyEval_EvalFrameEx() is called with throwflag=0. At exit, the exception state is now always restored or swapped, not only if why is WHY_YIELD or WHY_RETURN. Patch co-written with Antoine Pitrou.
1 parent fdc9953 commit 26f7b8a

3 files changed

Lines changed: 119 additions & 3 deletions

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‎Lib/test/test_generators.py‎

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Original file line numberDiff line numberDiff line change
@@ -50,6 +50,115 @@ def gen():
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self.assertEqual(gc.garbage, old_garbage)
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class ExceptionTest(unittest.TestCase):
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# Tests for the issue #23353: check that the currently handled exception
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# is correctly saved/restored in PyEval_EvalFrameEx().
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def test_except_throw(self):
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def store_raise_exc_generator():
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try:
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self.assertEqual(sys.exc_info()[0], None)
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yield
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except Exception as exc:
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# exception raised by gen.throw(exc)
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self.assertEqual(sys.exc_info()[0], ValueError)
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self.assertIsNone(exc.__context__)
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yield
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# ensure that the exception is not lost
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self.assertEqual(sys.exc_info()[0], ValueError)
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yield
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# we should be able to raise back the ValueError
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raise
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make = store_raise_exc_generator()
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next(make)
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try:
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raise ValueError()
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except Exception as exc:
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try:
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make.throw(exc)
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except Exception:
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pass
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next(make)
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with self.assertRaises(ValueError) as cm:
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next(make)
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self.assertIsNone(cm.exception.__context__)
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self.assertEqual(sys.exc_info(), (None, None, None))
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def test_except_next(self):
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def gen():
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self.assertEqual(sys.exc_info()[0], ValueError)
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yield "done"
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g = gen()
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try:
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raise ValueError
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except Exception:
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self.assertEqual(next(g), "done")
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self.assertEqual(sys.exc_info(), (None, None, None))
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def test_except_gen_except(self):
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def gen():
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try:
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self.assertEqual(sys.exc_info()[0], None)
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yield
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# we are called from "except ValueError:", TypeError must
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# inherit ValueError in its context
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raise TypeError()
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except TypeError as exc:
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self.assertEqual(sys.exc_info()[0], TypeError)
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self.assertEqual(type(exc.__context__), ValueError)
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# here we are still called from the "except ValueError:"
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self.assertEqual(sys.exc_info()[0], ValueError)
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yield
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self.assertIsNone(sys.exc_info()[0])
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yield "done"
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g = gen()
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next(g)
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try:
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raise ValueError
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except Exception:
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next(g)
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self.assertEqual(next(g), "done")
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self.assertEqual(sys.exc_info(), (None, None, None))
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def test_except_throw_exception_context(self):
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def gen():
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try:
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try:
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self.assertEqual(sys.exc_info()[0], None)
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yield
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except ValueError:
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# we are called from "except ValueError:"
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self.assertEqual(sys.exc_info()[0], ValueError)
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raise TypeError()
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except Exception as exc:
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self.assertEqual(sys.exc_info()[0], TypeError)
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self.assertEqual(type(exc.__context__), ValueError)
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# we are still called from "except ValueError:"
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self.assertEqual(sys.exc_info()[0], ValueError)
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yield
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self.assertIsNone(sys.exc_info()[0])
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yield "done"
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g = gen()
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next(g)
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try:
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raise ValueError
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except Exception as exc:
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g.throw(exc)
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self.assertEqual(next(g), "done")
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self.assertEqual(sys.exc_info(), (None, None, None))
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tutorial_tests = """
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Let's try a simple generator:
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‎Misc/NEWS‎

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Original file line numberDiff line numberDiff line change
@@ -50,6 +50,12 @@ Core and Builtins
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Library
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-------
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- Issue #23353: Fix the exception handling of generators in
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PyEval_EvalFrameEx(). At entry, save or swap the exception state even if
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PyEval_EvalFrameEx() is called with throwflag=0. At exit, the exception state
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is now always restored or swapped, not only if why is WHY_YIELD or
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WHY_RETURN. Patch co-written with Antoine Pitrou.
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- Issue #18518: timeit now rejects statements which can't be compiled outside
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a function or a loop (e.g. "return" or "break").
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‎Python/ceval.c‎

Lines changed: 4 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1189,8 +1189,8 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
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f->f_stacktop = NULL; /* remains NULL unless yield suspends frame */
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f->f_executing = 1;
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1192-
if (co->co_flags & CO_GENERATOR && !throwflag) {
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if (f->f_exc_type != NULL && f->f_exc_type != Py_None) {
1192+
if (co->co_flags & CO_GENERATOR) {
1193+
if (!throwflag && f->f_exc_type != NULL && f->f_exc_type != Py_None) {
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/* We were in an except handler when we left,
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restore the exception state which was put aside
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(see YIELD_VALUE). */
@@ -3172,7 +3172,8 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
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|| (retval == NULL && PyErr_Occurred()));
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fast_yield:
3175-
if (co->co_flags & CO_GENERATOR && (why == WHY_YIELD || why == WHY_RETURN)) {
3175+
if (co->co_flags & CO_GENERATOR) {
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/* The purpose of this block is to put aside the generator's exception
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state and restore that of the calling frame. If the current
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exception state is from the caller, we clear the exception values

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