Suppress exception chaining when PEP 3134 is merged

cat ioerror.stderr.old
Exception in thread Event Notifier:
Traceback (most recent call last):
  File "/usr/lib64/python3.3/site-packages/stem/control.py", line 1758, in get_network_status
    desc_content = self.get_info(query, get_bytes = True)
  File "/usr/lib64/python3.3/site-packages/stem/control.py", line 414, in wrapped
    raise exc
  File "/usr/lib64/python3.3/site-packages/stem/control.py", line 409, in wrapped
    return func(self, *args, **kwargs)
  File "/usr/lib64/python3.3/site-packages/stem/control.py", line 1113, in get_info
    raise exc
  File "/usr/lib64/python3.3/site-packages/stem/control.py", line 1066, in get_info
    stem.response.convert('GETINFO', response)
  File "/usr/lib64/python3.3/site-packages/stem/response/__init__.py", line 135, in convert
    message._parse_message(**kwargs)
  File "/usr/lib64/python3.3/site-packages/stem/response/getinfo.py", line 38, in _parse_message
    raise stem.InvalidArguments('552', 'GETINFO request contained unrecognized keywords: %s\n' % ', '.join(unrecognized_keywords), unrecognized_keywords)
stem.InvalidArguments: GETINFO request contained unrecognized keywords: ns/id/2BCDF9F0BCEFC2A44F7850F92362BA85AA226E1F


During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib64/python3.3/threading.py", line 901, in _bootstrap_inner
    self.run()
  File "/usr/lib64/python3.3/threading.py", line 858, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib64/python3.3/site-packages/stem/control.py", line 882, in _event_loop
    self._handle_event(event_message)
  File "/usr/lib64/python3.3/site-packages/stem/control.py", line 3480, in _handle_event
    listener(event_message)
  File "./err.py", line 47, in orconn_event
    relay = controller.get_network_status(fingerprint)
  File "/usr/lib64/python3.3/site-packages/stem/control.py", line 414, in wrapped
    raise exc
  File "/usr/lib64/python3.3/site-packages/stem/control.py", line 409, in wrapped
    return func(self, *args, **kwargs)
  File "/usr/lib64/python3.3/site-packages/stem/control.py", line 1761, in get_network_status
    raise stem.DescriptorUnavailable("Tor was unable to provide the descriptor for '%s'" % relay)
stem.DescriptorUnavailable: Tor was unable to provide the descriptor for '2BCDF9F0BCEFC2A44F7850F92362BA85AA226E1F'

$ cat err.py
#!/usr/bin/python3 -u

#   Toralf Foerster
#   Hamburg
#   Germany

# collect data wrt to https://trac.torproject.org/projects/tor/ticket/13603
#

import time
import functools

from stem import ORStatus, ORClosureReason
from stem.control import EventType, Controller


def main():
  class Cnt(object):
    def __init__(self, done=0, closed=0, ioerror=0):
      self.done = done
      self.closed = closed
      self.ioerror = ioerror

  c = Cnt()

  with Controller.from_port(port=9051) as controller:
    controller.authenticate()

    orconn_listener = functools.partial(orconn_event, controller, c)
    controller.add_event_listener(orconn_listener, EventType.ORCONN)

    while True:
      time.sleep(1)

def orconn_event(controller, c, event):
  if event.status == ORStatus.CLOSED:
    c.closed += 1

    if event.reason == ORClosureReason.DONE:
      c.done += 1

    if event.reason == ORClosureReason.IOERROR:
      c.ioerror += 1

      fingerprint = event.endpoint_fingerprint
      print (" %i %i %i %i %s %40s" % (c.closed, c.done, c.ioerror, event.arrived_at, time.ctime(event.arrived_at), fingerprint), end='')
      relay = controller.get_network_status(fingerprint)
      if relay:
        print (" %15s %5i %s %s" % (relay.address, relay.or_port, controller.get_info("ip-to-country/%s" % relay.address, 'unknown'), relay.nickname), end='')
      print ('', flush=True)

if __name__ == '__main__':
  main()