Tornado Traceback: Exception in callback tornado.stack_context._StackContextWrapper object

gistfile1.pytb

ERROR:root:Exception in callback <tornado.stack_context._StackContextWrapper object at 0x000000002054c1a8>
Traceback (most recent call last):
  File "/usr/local/lib/pypy2.7/dist-packages/tornado/ioloop.py", line 421, in _run_callback
    callback()
  File "/usr/lib/pypy/lib_pypy/_functools.py", line 22, in __call__
    return self.func(*(self.args + fargs), **fkeywords)
  File "/usr/local/lib/pypy2.7/dist-packages/tornado/iostream.py", line 305, in wrapper
    callback(*args)
  File "/usr/lib/pypy/lib_pypy/_functools.py", line 22, in __call__
    return self.func(*(self.args + fargs), **fkeywords)
  File "/usr/local/lib/pypy2.7/dist-packages/tornado/httpserver.py", line 268, in _on_headers
    self.request_callback(self._request)
  File "/usr/local/lib/pypy2.7/dist-packages/tornado/web.py", line 1427, in __call__
    handler._execute(transforms, *args, **kwargs)
  File "/usr/local/lib/pypy2.7/dist-packages/tornado/web.py", line 1046, in _execute
    self._handle_request_exception(e)
  File "/usr/local/lib/pypy2.7/dist-packages/tornado/web.py", line 1086, in _handle_request_exception
    self.send_error(500, exc_info=sys.exc_info())
  File "/usr/local/lib/pypy2.7/dist-packages/tornado/web.py", line 741, in send_error
    self.finish()
  File "/usr/local/lib/pypy2.7/dist-packages/tornado/web.py", line 721, in finish
    self.flush(include_footers=True)
  File "/usr/local/lib/pypy2.7/dist-packages/tornado/web.py", line 681, in flush
    self.request.write(headers + chunk, callback=callback)
  File "/usr/local/lib/pypy2.7/dist-packages/tornado/httpserver.py", line 418, in write
    self.connection.write(chunk, callback=callback)
  File "/usr/local/lib/pypy2.7/dist-packages/tornado/httpserver.py", line 183, in write
    assert self._request, "Request closed"
AssertionError: Request closed