Add a few more docstrings about ytrss.

ycdl/objects.py

@@ -32,6 +32,13 @@ class Channel(Base):
         return f'Channel:{self.id}'
 
     def _rss_assisted_videos(self):
+        '''
+        RSS-assisted refresh will use the channel's RSS feed to find videos
+        that are newer than the most recent video we have in the database.
+        Then, these new videos can be queried using the regular API since the
+        RSS doesn't contain all the attributes we need. This saves us from
+        wasting any metered API calls in the case that the RSS has nothing new.
+        '''
         try:
             most_recent_video = self.get_most_recent_video_id()
         except exceptions.NoVideos as exc:

ycdl/ytrss.py

@@ -21,12 +21,20 @@ def _get_user_videos(channel_id):
     return video_ids
 
 def get_user_videos(channel_id):
+    '''
+    Return the list of video ids from the channel.
+    Expect a maximum of 15 results.
+    '''
     try:
         return _get_user_videos(channel_id)
     except Exception:
         raise exceptions.RSSAssistFailed(f'Failed to fetch RSS videos.') from exc
 
 def get_user_videos_since(channel_id, video_id):
+    '''
+    Return the list of video ids that are more recently released than the
+    reference id.
+    '''
     video_ids = get_user_videos(channel_id)
     try:
         index = video_ids.index(video_id)