*Generate a file prefix based on the type of search for saving files to disk*

        **Return:**
            - ``prefix`` -- the file prefix

def _file_prefix(
            self):
        """*Generate a file prefix based on the type of search for saving files to disk*

        **Return:**
            - ``prefix`` -- the file prefix
        """
        self.log.info('starting the ``_file_prefix`` method')

        if self.ra:
            now = datetime.now()
            prefix = now.strftime("%Y%m%dt%H%M%S%f_tns_conesearch_")
        elif self.name:
            prefix = self.name + "_tns_conesearch_"
        elif self.internal_name:
            prefix = self.internal_name + "_tns_conesearch_"
        elif self.discInLastDays:
            discInLastDays = str(self.discInLastDays)
            now = datetime.now()
            prefix = now.strftime(
                discInLastDays + "d_since_%Y%m%d_tns_conesearch_")

        self.log.info('completed the ``_file_prefix`` method')
        return prefix