How to use the yagmail.compat.text_type function in yagmail

def prepare_message(user, useralias, addresses, subject, contents, attachments, headers, encoding, newline_to_break=True):
    # check if closed!!!!!! XXX
    """ Prepare a MIME message """
    if isinstance(contents, text_type):
        contents = [contents]
    if isinstance(attachments, text_type):
        attachments = [attachments]

    # merge contents and attachments for now.
    if attachments is not None:
        for a in attachments:
            if not os.path.isfile(a):
                raise TypeError("'{0}' is not a valid filepath".format(a))
        contents = attachments if contents is None else contents + attachments

    has_included_images, content_objects = prepare_contents(contents, encoding)
    msg = MIMEMultipart()
    if headers is not None:
        # Strangely, msg does not have an update method, so then manually.
        for k, v in headers.items():

def prepare_message(user, useralias, addresses, subject, contents, attachments, headers, encoding, newline_to_break=True):
    # check if closed!!!!!! XXX
    """ Prepare a MIME message """
    if isinstance(contents, text_type):
        contents = [contents]
    if isinstance(attachments, text_type):
        attachments = [attachments]

    # merge contents and attachments for now.
    if attachments is not None:
        for a in attachments:
            if not os.path.isfile(a):
                raise TypeError("'{0}' is not a valid filepath".format(a))
        contents = attachments if contents is None else contents + attachments

    has_included_images, content_objects = prepare_contents(contents, encoding)
    msg = MIMEMultipart()
    if headers is not None:
        # Strangely, msg does not have an update method, so then manually.
        for k, v in headers.items():
            msg[k] = v
    if headers is None or "Date" not in headers: