bpo-34588: Fix an off-by-one error in traceback formatting. (GH-9077)
The recursive frame pruning code always undercounted the number of elided frames by one. That is, in the "[Previous line repeated N more times]" message, N would always be one too few. Near the recursive pruning cutoff, one frame could be silently dropped. That situation is demonstrated in the OP of the bug report. The fix is to start the identical frame counter at 1.
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@ -373,7 +373,7 @@ class TracebackFormatTests(unittest.TestCase):
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' return g(count-1)\n'
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f' File "{__file__}", line {lineno_g+2}, in g\n'
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' return g(count-1)\n'
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' [Previous line repeated 6 more times]\n'
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' [Previous line repeated 7 more times]\n'
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f' File "{__file__}", line {lineno_g+3}, in g\n'
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' raise ValueError\n'
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'ValueError\n'
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@ -412,7 +412,7 @@ class TracebackFormatTests(unittest.TestCase):
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' return h(count-1)\n'
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f' File "{__file__}", line {lineno_h+2}, in h\n'
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' return h(count-1)\n'
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' [Previous line repeated 6 more times]\n'
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' [Previous line repeated 7 more times]\n'
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f' File "{__file__}", line {lineno_h+3}, in h\n'
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' g()\n'
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)
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@ -420,6 +420,63 @@ class TracebackFormatTests(unittest.TestCase):
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actual = stderr_h.getvalue().splitlines()
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self.assertEqual(actual, expected)
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# Check the boundary conditions. First, test just below the cutoff.
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with captured_output("stderr") as stderr_g:
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try:
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g(traceback._RECURSIVE_CUTOFF)
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except ValueError as exc:
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render_exc()
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else:
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self.fail("no error raised")
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result_g = (
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f' File "{__file__}", line {lineno_g+2}, in g\n'
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' return g(count-1)\n'
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f' File "{__file__}", line {lineno_g+2}, in g\n'
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' return g(count-1)\n'
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f' File "{__file__}", line {lineno_g+2}, in g\n'
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' return g(count-1)\n'
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f' File "{__file__}", line {lineno_g+3}, in g\n'
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' raise ValueError\n'
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'ValueError\n'
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)
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tb_line = (
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'Traceback (most recent call last):\n'
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f' File "{__file__}", line {lineno_g+71}, in _check_recursive_traceback_display\n'
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' g(traceback._RECURSIVE_CUTOFF)\n'
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)
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expected = (tb_line + result_g).splitlines()
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actual = stderr_g.getvalue().splitlines()
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self.assertEqual(actual, expected)
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# Second, test just above the cutoff.
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with captured_output("stderr") as stderr_g:
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try:
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g(traceback._RECURSIVE_CUTOFF + 1)
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except ValueError as exc:
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render_exc()
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else:
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self.fail("no error raised")
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result_g = (
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f' File "{__file__}", line {lineno_g+2}, in g\n'
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' return g(count-1)\n'
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f' File "{__file__}", line {lineno_g+2}, in g\n'
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' return g(count-1)\n'
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f' File "{__file__}", line {lineno_g+2}, in g\n'
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' return g(count-1)\n'
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' [Previous line repeated 1 more time]\n'
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f' File "{__file__}", line {lineno_g+3}, in g\n'
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' raise ValueError\n'
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'ValueError\n'
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)
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tb_line = (
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'Traceback (most recent call last):\n'
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f' File "{__file__}", line {lineno_g+99}, in _check_recursive_traceback_display\n'
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' g(traceback._RECURSIVE_CUTOFF + 1)\n'
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)
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expected = (tb_line + result_g).splitlines()
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actual = stderr_g.getvalue().splitlines()
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self.assertEqual(actual, expected)
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def test_recursive_traceback_python(self):
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self._check_recursive_traceback_display(traceback.print_exc)
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@ -310,6 +310,8 @@ def walk_tb(tb):
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tb = tb.tb_next
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_RECURSIVE_CUTOFF = 3 # Also hardcoded in traceback.c.
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class StackSummary(list):
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"""A stack of frames."""
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@ -398,18 +400,21 @@ class StackSummary(list):
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last_name = None
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count = 0
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for frame in self:
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if (last_file is not None and last_file == frame.filename and
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last_line is not None and last_line == frame.lineno and
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last_name is not None and last_name == frame.name):
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count += 1
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else:
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if count > 3:
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result.append(f' [Previous line repeated {count-3} more times]\n')
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if (last_file is None or last_file != frame.filename or
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last_line is None or last_line != frame.lineno or
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last_name is None or last_name != frame.name):
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if count > _RECURSIVE_CUTOFF:
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count -= _RECURSIVE_CUTOFF
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result.append(
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f' [Previous line repeated {count} more '
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f'time{"s" if count > 1 else ""}]\n'
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)
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last_file = frame.filename
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last_line = frame.lineno
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last_name = frame.name
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count = 0
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if count >= 3:
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count += 1
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if count > _RECURSIVE_CUTOFF:
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continue
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row = []
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row.append(' File "{}", line {}, in {}\n'.format(
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@ -420,8 +425,12 @@ class StackSummary(list):
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for name, value in sorted(frame.locals.items()):
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row.append(' {name} = {value}\n'.format(name=name, value=value))
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result.append(''.join(row))
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if count > 3:
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result.append(f' [Previous line repeated {count-3} more times]\n')
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if count > _RECURSIVE_CUTOFF:
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count -= _RECURSIVE_CUTOFF
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result.append(
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f' [Previous line repeated {count} more '
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f'time{"s" if count > 1 else ""}]\n'
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)
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return result
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@ -0,0 +1,2 @@
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Fix an off-by-one in the recursive call pruning feature of traceback
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formatting.
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@ -511,16 +511,21 @@ tb_displayline(PyObject *f, PyObject *filename, int lineno, PyObject *name)
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return err;
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}
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static const int TB_RECURSIVE_CUTOFF = 3; // Also hardcoded in traceback.py.
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static int
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tb_print_line_repeated(PyObject *f, long cnt)
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{
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int err;
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cnt -= TB_RECURSIVE_CUTOFF;
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PyObject *line = PyUnicode_FromFormat(
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" [Previous line repeated %ld more times]\n", cnt-3);
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(cnt > 1)
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? " [Previous line repeated %ld more times]\n"
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: " [Previous line repeated %ld more time]\n",
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cnt);
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if (line == NULL) {
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return -1;
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}
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err = PyFile_WriteObject(line, f, Py_PRINT_RAW);
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int err = PyFile_WriteObject(line, f, Py_PRINT_RAW);
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Py_DECREF(line);
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return err;
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}
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@ -544,15 +549,11 @@ tb_printinternal(PyTracebackObject *tb, PyObject *f, long limit)
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tb = tb->tb_next;
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}
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while (tb != NULL && err == 0) {
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if (last_file != NULL &&
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tb->tb_frame->f_code->co_filename == last_file &&
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last_line != -1 && tb->tb_lineno == last_line &&
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last_name != NULL && tb->tb_frame->f_code->co_name == last_name)
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{
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cnt++;
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}
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else {
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if (cnt > 3) {
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if (last_file == NULL ||
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tb->tb_frame->f_code->co_filename != last_file ||
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last_line == -1 || tb->tb_lineno != last_line ||
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last_name == NULL || tb->tb_frame->f_code->co_name != last_name) {
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if (cnt > TB_RECURSIVE_CUTOFF) {
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err = tb_print_line_repeated(f, cnt);
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}
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last_file = tb->tb_frame->f_code->co_filename;
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@ -560,7 +561,8 @@ tb_printinternal(PyTracebackObject *tb, PyObject *f, long limit)
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last_name = tb->tb_frame->f_code->co_name;
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cnt = 0;
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}
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if (err == 0 && cnt < 3) {
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cnt++;
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if (err == 0 && cnt <= TB_RECURSIVE_CUTOFF) {
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err = tb_displayline(f,
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tb->tb_frame->f_code->co_filename,
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tb->tb_lineno,
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@ -571,7 +573,7 @@ tb_printinternal(PyTracebackObject *tb, PyObject *f, long limit)
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}
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tb = tb->tb_next;
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}
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if (err == 0 && cnt > 3) {
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if (err == 0 && cnt > TB_RECURSIVE_CUTOFF) {
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err = tb_print_line_repeated(f, cnt);
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}
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return err;
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