code: def replace(self, lkey, lval, db=None):
          '''
          Like put, but returns the previous value if existed
          '''
          return self._xact_action(self.replace, lmdb.Transaction.replace, lkey, lval, db=dbf replace(self, lkey, lval, db=None):
          '''
          Like put, but returns the previous value if existed
          '''
          return self._xact_action(self.replace, lmdb.Transaction.replace, lkey, lval, db=db)
docs: Like put, but returns the previous value if existed