code: def convert(self, request, response, data):
          
  
          size = response.content_length
          if not size:
              size = "-" if self.conv_chr == 'b' else 0
  
          return str(size)
docs: Performs the desired Conversion.
  
          :param request: The webob Request object describing the
                          request.
          :param response: The webob Response object describing the
                           response.
          :param data: The data dictionary returned by the prepare()
                       method.
  
          :returns: A string, the results of which are the desired
                    conversion.