while comment_feed is not None:
    for comment in comment_feed.entry:
        yield comment
next_link = comment_feed.GetNextLink()
if next_link is None:
    comment_feed = None
else:
    comment_feed = client.GetYouTubeVideoCommentFeed(next_link.href)
client = service.YouTubeService()
client.ClientLogin(USERNAME, PASSWORD)
for comment in comments_generator(client, VIDEO_ID):
    author_name = comment.author[0].name.text
text = comment.content.text
print('{}: {}'.format(author_name, text))
How to get all YouTube comments with Python's gdata module?