def METHOD_NAME(self, ex):
    '''
    Formats training prompt based on self.input_field_type
    Training example: 
        e.g. response: <response> # input_label_type = response
        e.g. utterance: <utterance> # input_label_type = utterance
        e.g. passage: <passage> utterance: <utterance> # input_label_type = passage+utterance
    '''
    ex["labels"]["utterance"] = ex["utterance"]
    parts = self.input_label_type.split('+')
    input_sentence = ' '.join([part + ': ' + ex["labels"][part] for part in parts])
    return input_sentence