code: def _substitute(self, query, model_class=None):
          '''
          Replaces $db and $table placeholders in the query.
          '''
          if '$' in query:
              mapping = dict(db="`%s`" % self.db_name)
              if model_class:
                  mapping['table'] = "`%s`.`%s`" % (self.db_name, model_class.table_name())
              query = Template(query).safe_substitute(mapping)
          return querf _substitute(self, query, model_class=None):
          '''
          Replaces $db and $table placeholders in the query.
          '''
          if '$' in query:
              mapping = dict(db="`%s`" % self.db_name)
              if model_class:
                  mapping['table'] = "`%s`.`%s`" % (self.db_name, model_class.table_name())
              query = Template(query).safe_substitute(mapping)
          return query
docs: Replaces $db and $table placeholders in the query.