'Populate the stanza object using an optional XML object.
Overrides ElementBase.setup.
Sets a default error type and condition, and changes the
parent stanza\'s type to \'error\'.
Arguments:
xml -- Use an existing XML object for the stanza\'s values.'

def setup(self, xml=None):

    self.namespace = Failure.namespace
    if StanzaBase.setup(self, xml):
        self['condition'] = 'not-authorized'
    self.xml.tag = self.tag_name()
