[issue14369] make __closure__ writable

[Richard Oudkerk]

Richard Oudkerk <shibturn at gmail.com> added the comment:

The patch causes crashes.  If I define

  def cell(o):
    def f(): o
    return f.__closure__[0]

  def f():
    a = 1
    b = 2
    def g():
      return a + b
    return g

  g = f()

then I find

  g.__closure__ = None; g()                          -> crash
  g.__closure__ = (cell(3),); g()                    -> crash
  g.__closure__ = (1, 2); g()                        -> SystemError *
  g.__closure__ = (cell(3), cell(4), cell(5)); g()   -> returns 7

* SystemError: ..\Objects\cellobject.c:24: bad argument to internal function

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue14369>
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