Decorator for timing out a method that returns a twisted deferred.

twisted_timeout.py

def timeout(seconds=5, error_type=None, error_message=None):
  """
  Attaches a timeout to the deferred returned by the wrapped function.
  After timeout seconds the deferred is canceled and an exception raised.
  """
  def attach_timeout(method):
    @functools.wraps(method)
    def wrapper(self, *args, **kwargs):
        d = method(self, *args, **kwargs)
        def on_timeout():
          if not d.called:
            if error_type:
              d.errback(error_type(error_message))
            d.cancel()
        reactor.callLater(seconds, on_timeout)          
        return d
    return wrapper
  return attach_timeout

# Example
@timeout(20, ExternalStorageException, 'cassandra fetch timeout')
@defer.inlineCallbacks
def cass_get(self, key, column_family):
  pass