__all__ = ['Blog', 'Post', 'Topic', 'TopicAssociation', 'Comment']import datetimefrom testlib.compat import *class Blog(object):    def __init__(self, owner=None):        self.owner = ownerclass Post(object):    topics = set    def __init__(self, user=None, headline=None, summary=None):        self.user = user        self.datetime = datetime.datetime.today()        self.headline = headline        self.summary = summary        self.comments = []        self.comment_count = 0class Topic(object):    def __init__(self, keyword=None, description=None):        self.keyword = keyword        self.description = descriptionclass TopicAssociation(object):    def __init__(self, post=None, topic=None, is_primary=False):        self.post = post        self.topic = topic        self.is_primary = is_primaryclass Comment(object):    def __init__(self, subject=None, body=None):        self.subject = subject        self.datetime = datetime.datetime.today()        self.body = body