logging.shutdown includes a try/except block to avoid emitting spurious IO errors while the interpreter is shutting down. This fails if a registered handler tries to do IO (such as calling flush()) in its release method.

It would be better if the flush-and-close block was written as:

  try:
      hr.acquire()
      try:
          hr.flush()
          hr.close()
      finally:
          hr.release()
  except (IOError, ValueError):
    # Tolerate handlers that try to do IO in release()