'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'

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,)))
