def parse_hash_comment(file_path):
    """
    Read file with given file_path line by line,
    return the first line that starts with "# SHA1:", like this:

        # SHA1:da39a3ee5e6b4b0d3255bfef95601890afd80709
    """
    with open(file_path) as fp:
        for line in fp:
            if line.startswith("# SHA1:"):
                return line
    return None