[issue10582] PyErr_PrintEx exits silently when passed SystemExit exception

[Irit Katriel]

Irit Katriel  added the comment:

This was removed in https://github.com/python/cpython/pull/13390.

--
nosy: +iritkatriel
resolution:  -> out of date
stage:  -> resolved
status: open -> closed

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[issue10582] PyErr_PrintEx exits silently when passed SystemExit exception

[Mark Lawrence]

Change by Mark Lawrence :


--
nosy:  -BreamoreBoy

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[issue10582] PyErr_PrintEx exits silently when passed SystemExit exception

[STINNER Victor]

Changes by STINNER Victor :


--
nosy: +haypo

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[issue10582] PyErr_PrintEx exits silently when passed SystemExit exception

[Mark Lawrence]

Mark Lawrence added the comment:

@Marc please accept our apologies for having missed this. Can you still 
reproduce the problem?

--
nosy: +BreamoreBoy
versions: +Python 2.7, Python 3.4, Python 3.5 -Python 2.6

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[issue10582] PyErr_PrintEx exits silently when passed SystemExit exception

[Marc Horowitz]

New submission from Marc Horowitz :

I discovered this bug working with panda3d.  I've attached a short
python script which demonstrates the problem.  After installing
panda3d, run the script, and then hit q in the window which appears.
You'll see that none of the cleanup code after the 'run()' main loop
runs.

The underlying cause is in how panda3d uses the C API.  It's got code
like this (in src/pipeline/thread.cxx):

// Call the user's function.
result = PyObject_Call(function, args, NULL);
if (result == (PyObject *)NULL && PyErr_Occurred()) {
  // We got an exception.  Move the exception from the current
  // thread into the main thread, so it can be handled there.
  PyObject *exc, *val, *tb;
  PyErr_Fetch(&exc, &val, &tb);

  thread_cat.error()
<< "Exception occurred within " << *this << "\n";

  // Temporarily restore the exception state so we can print a
  // callback on-the-spot.
  Py_XINCREF(exc);
  Py_XINCREF(val);
  Py_XINCREF(tb);
  PyErr_Restore(exc, val, tb);
  PyErr_Print();

  ...

If the code being called (generally a panda3d task function or event
handler) calls sys.exit, the PyErr_Print() never returns.  This is
surprising, as the the documentation never mentions that a function
with an innocuous name like "Print" might never return.  

However, I don't think this is a panda3d bug; I think that the
function as documented is the way it should behave.  Otherwise, the
vast majority of calls to this method will need to look like

if (!PyErr_ExceptionMatches(PyExc_SystemExit)) {
  PyErr_PrintEx(1);
}

which seems like a poor abstraction.

Another unexpected side effect is when python is used with the -i
flag.  Because of the way this alters the normal exit behavior, the
code runs the way I'd expect, and the cleanup code in the test
application *does* run.  It seems rather strange to me that cleanup
code should run or not run based on the -i flag.

I believe the fix for all this is that PyErr_PrintEx be changed to
behave as documented, *not* call handle_system_exit() when passed
SystemExit, and instead in the places where the interpreter main loop
is run, followed by PyErr_PrintEx(), that SystemExit is special cased
in those specific locations as needed.

--
components: Interpreter Core
files: exit_test.py
messages: 122846
nosy: Marc.Horowitz
priority: normal
severity: normal
status: open
title: PyErr_PrintEx exits silently when passed SystemExit exception
type: behavior
versions: Python 2.6
Added file: http://bugs.python.org/file19875/exit_test.py

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