code: def get_pre_alter_table_index_foreign_key_sql(self, diff):
          
          if not isinstance(diff.from_table, Table):
              raise DBALException(
                  "Sqlite platform requires for alter table the table"
                  "diff with reference to original table schema"
              )
  
          sql = []
          for index in diff.from_table.get_indexes().values():
              if not index.is_primary():
                  sql.append(self.get_drop_index_sql(index, diff.name))
  
          return sql
docs: :param diff: The table diff
          :type diff: orator.dbal.table_diff.TableDiff
  
          :rtype: list