Format bytes for printing

    :param data: Bytes
    :type data: None | bytearray | str
    :return: Printable version
    :rtype: unicode

def format_data(data):
    """
    Format bytes for printing

    :param data: Bytes
    :type data: None | bytearray | str
    :return: Printable version
    :rtype: unicode
    """
    if data is None:
        return None
    return u":".join([u"{:02x}".format(ord(c)) for c in data])