text: from django.core.signals import got_request_exception
  
  from concurrency.config import conf
  from concurrency.exceptions import RecordModifiedError
  
  try:
      from django.urls.utils import get_callable
  except ImportError:
      from django.core.urlresolvers import get_callable
  
  
  class ConcurrencyMiddleware(object):
      """ Intercept :ref:`RecordModifiedError` and invoke a callable defined in
      :setting:`CONCURRECY_HANDLER409` passing the request and the object.
  
      """
  
      def __init__(self, get_response=None):
          self.get_response = get_response
  
      def __call__(self, request):
          response = self.get_response(request)
          return response
  
      def process_exception(self, request, exception):
          if isinstance(exception, RecordModifiedError):
              got_request_exception.send(sender=self, request=request)
              callback = get_callable(conf.HANDLER409)
              return callback(request, target=exception.target)
          else:  # pragma: no cover
              pass
  