(cls)
Should return a list of field names that are the keys in
        the extra_fields dict.
Should return a list of field names that are the keys in
        the extra_fields dict.
Should return a list of field names that are the keys in the extra_fields dict .
def get_available_extra_fields(cls):
        """
        Should return a list of field names that are the keys in
        the extra_fields dict.
        """
        raise NotImplementedError("Please implement this method")
def get_available_extra_fields ( cls ) : raise NotImplementedError ( "Please implement this method" )