How to use the pydoctor.zopeinterface.ZopeInterfaceSystem function in pydoctor

if self.decorators:
            getDeprecated(self, list(self.decorators))

        for x in super(TwistedFunction, self).docsources():
            yield x



class TwistedASTBuilder(zopeinterface.ZopeInterfaceASTBuilder):
    # Vistor is not a typo...
    ModuleVistor = TwistedModuleVisitor



class TwistedSystem(zopeinterface.ZopeInterfaceSystem):
    """
    A PyDoctor "system" used to generate the docs.
    """
    defaultBuilder = TwistedASTBuilder
    Function = TwistedFunction

    def __init__(self, options=None):
        super(TwistedSystem, self).__init__(options=options)
        # Use custom SphinxInventory so that we can resolve valid L{} markup
        # for which the Sphinx inventory is not published or broken.
        self.intersphinx = TwistedSphinxInventory(
            logger=self.msg, project_name=self.projectname)


    def privacyClass(self, documentable):
        """

"""
        Get are HEAD response for URL.

        Here to help with testing and allow injecting another URL getter.

        @param url: Full URL to the page which is retrieved.
        @type url: L{str}

        @return: The response for the HEAD method.
        @rtype: urllib2 response
        """
        return urllib2.urlopen(HeadRequest(url))



class TwistedSystem(zopeinterface.ZopeInterfaceSystem):
    """
    Maybe class used to set up all pydoctor system.
    """

    def __init__(self, options=None):
        super(TwistedSystem, self).__init__(options=options)
        # Use custom SphinxInventory so that we can resolve valid L{} markup
        # for which the Sphinx inventory is not published or broken.
        self.intersphinx = TwistedSphinxInventory(
            logger=self.msg, project_name=self.projectname)


    def privacyClass(self, documentable):
        """
        Report the privacy level for an object.