<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def set_field(self, field_name, field_val=None):
 """ set a field into .fields attribute n insert/update queries, these are the fields that will be inserted/updated into the db """

        field_name = self._normalize_field_name(field_name)
        self.fields_set.append(field_name, [field_name, field_val])
        return self