def _dotUnquoter(line):
    """
    Remove a byte-stuffed termination character at the beginning of a line if
    present.

    When the termination character (C{'.'}) appears at the beginning of a line,
    the server byte-stuffs it by adding another termination character to
    avoid confusion with the terminating sequence (C{'.\\r\\n'}).

    @type line: L{bytes}
    @param line: A received line.

    @rtype: L{bytes}
    @return: The line without the byte-stuffed termination character at the
        beginning if it was present. Otherwise, the line unchanged.
    """
    if line.startswith(b'..'):
        return line[1:]
    return line

    Remove a byte-stuffed termination character at the beginning of a line if
    present.

    When the termination character (C{'.'}) appears at the beginning of a line,
    the server byte-stuffs it by adding another termination character to
    avoid confusion with the terminating sequence (C{'.\r\n'}).

    @type line: L{bytes}
    @param line: A received line.

    @rtype: L{bytes}
    @return: The line without the byte-stuffed termination character at the
        beginning if it was present. Otherwise, the line unchanged.
    
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/pop3client.py