code: def collections(self):
          
          from .collection import Collection
  
          if self.url is None or self.collection_num == 0:
              return
          else:
              collection_num = self.collection_num
              for page_index in range(1, (collection_num - 1) // 20 + 2):
                  html = self._session.get(
                      self.url + 'collections?page=' + str(page_index)).text
                  soup = BeautifulSoup(html)
                  collections_names = soup.find_all(
                      'a', class_='zm-profile-fav-item-title')
                  collection_follower_nums = soup.find_all(
                      'div', class_='zm-profile-fav-bio')
                  for c, f in zip(collections_names, collection_follower_nums):
                      c_url = Zhihu_URL + c['href']
                      c_name = c.text
                      c_fn = int(re_get_number.match(f.contents[2]).group(1))
                      yield Collection(c_url, self, c_name, c_fn,
                                       session=self._session)
docs: 获取用户收藏夹.
  
          :return: 用户收藏夹，返回生成器
          :rtype: Collection.Iterable