<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def iter_comments_on_commit(self, sha, number=1, etag=None):
 """Iterate over comments for a single commit. :param sha: (required), sha of the commit to list comments on :type sha: str :param int number: (optional), number of comments to return. Default: -1 returns all comments :param str etag: (optional), ETag from a previous request to the same endpoint :returns: generator of :class:`RepoComment <github3.repos.comment.RepoComment>`\ s """

        url = self._build_url('commits', sha, 'comments', base_url=self._api)
        return self._iter(int(number), url, RepoComment, etag=etag)