code: def getSingle(self, type_uri, default=None):
          
          values = self.data.get(type_uri)
          if not values:
              return default
          elif len(values) == 1:
              return values[0]
          else:
              raise AXError(
                  'More than one value present for %r' % (type_uri,))
docs: Get a single value for an attribute. If no value was sent
          for this attribute, use the supplied default. If there is more
          than one value for this attribute, this method will fail.
  
          @type type_uri: str
          @param type_uri: The URI for the attribute
  
          @param default: The value to return if the attribute was not
              sent in the fetch_response.
  
          @returns: The value of the attribute in the fetch_response
              message, or the default supplied
          @rtype: unicode or NoneType
  
          @raises ValueError: If there is more than one value for this
              parameter in the fetch_response message.
          @raises KeyError: If the attribute was not sent in this response