def client_comments_file_path(revision, filename):
    """Build a path with this pattern: client_comments/<document number>_<revision name>_comments.{ext>"""
    return (
        "client_comments/{document_number}_{revision_name}_comments.{extension}".format(
            document_number=revision.document,
            revision_name=revision.name,
            extension=filename.split(".")[-1],
        )
    )