<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def encode(self, data, serializer=None):
 """ Serialize a data structure into a string suitable for sending as an AMQP message body. :param data: The message data to send. Can be a list, dictionary or a string. :keyword serializer: An optional string representing the serialization method you want the data marshalled into. (For example, ``json``, ``raw``, or ``pickle``). If ``None`` (default), then `JSON`_ will be used, unless ``data`` is a ``str`` or ``unicode`` object. In this latter case, no serialization occurs as it would be unnecessary. Note that if ``serializer`` is specified, then that serialization method will be used even if a ``str`` or ``unicode`` object is passed in. :returns: A three-item tuple containing the content type (e.g., ``application/json``), content encoding, (e.g., ``utf-8``) and a string containing the serialized data. :raises SerializerNotInstalled: If the serialization method requested is not available. """

        if serializer == "raw":
            return raw_encode(data)
        if serializer and not self._encoders.get(serializer):
            raise SerializerNotInstalled(
                        "No encoder installed for %s" % serializer)

        # If a raw string was sent, assume binary encoding
        # (it's likely either ASCII or a raw binary file, but 'binary'
        # charset will encompass both, even if not ideal.
        if not serializer and isinstance(data, str):
            # In Python 3+, this would be "bytes"; allow binary data to be
            # sent as a message without getting encoder errors
            return "application/data", "binary", data

        # For unicode objects, force it into a string
        if not serializer and isinstance(data, unicode):
            payload = data.encode("utf-8")
            return "text/plain", "utf-8", payload

        if serializer:
            content_type, content_encoding, encoder = \
                    self._encoders[serializer]
        else:
            encoder = self._default_encode
            content_type = self._default_content_type
            content_encoding = self._default_content_encoding

        payload = encoder(data)
        return content_type, content_encoding, payload