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:rtype: Topic.Iterable'

@property
def followed_topics(self):

    from .topic import Topic
    if (self.url is None):
        return
    if (self.followed_topic_num > 0):
        tag = self.soup.find('div', class_='zm-profile-side-topics')
        if (tag is not None):
            for a in tag.find_all('a'):
                (yield Topic((Zhihu_URL + a['href']), a.img['alt'], session=self._session))
        if (self.followed_topic_num > 7):
            offset = 7
            gotten_data_num = 20
            while (gotten_data_num == 20):
                data = {'start': 0, 'offset': offset, '_xsrf': self.xsrf}
                j = self._session.post(Author_Get_More_Follow_Topic_URL.format(self.id), data=data).json()
                gotten_data_num = j['msg'][0]
                offset += gotten_data_num
                topic_item = BeautifulSoup(j['msg'][1]).find_all('div', class_='zm-profile-section-item')
                for div in topic_item:
                    name = div.strong.text
                    url = (Zhihu_URL + div.a['href'])
                    (yield Topic(url, name, session=self._session))
