def process(self, stack, stmt):
        if isinstance(stmt, sql.Statement):
            self._curr_stmt = stmt
        self._process(stmt)
        if isinstance(stmt, sql.Statement):
            if self._last_stmt is not None:
                if unicode(self._last_stmt).endswith('\n'):
                    nl = '\n'
                else:
                    nl = '\n\n'
                stmt.tokens.insert(
                    0, sql.Token(T.Whitespace, nl))
            if self._last_stmt != stmt:
                self._last_stmt = stmt


# FIXME: Doesn't work ;) 

def process(self, stack, stmt):
        if isinstance(stmt, sql.Statement):
            self._curr_stmt = stmt
        self._process(stmt)
        if isinstance(stmt, sql.Statement):
            if self._last_stmt is not None:
                if str(self._last_stmt).endswith('\n'):
                    nl = '\n'
                else:
                    nl = '\n\n'
                stmt.tokens.insert(
                    0, sql.Token(T.Whitespace, nl))
            if self._last_stmt != stmt:
                self._last_stmt = stmt


# FIXME: Doesn't work ;) 

def parse_search_filter(cls, filter_string):
        if not filter_string:
            return []
        try:
            parsed = sqlparse.parse(filter_string)
        except Exception:
            raise MlflowException("Error on parsing filter '%s'" % filter_string,
                                  error_code=INVALID_PARAMETER_VALUE)
        if len(parsed) == 0 or not isinstance(parsed[0], Statement):
            raise MlflowException("Invalid filter '%s'. Could not be parsed." %
                                  filter_string, error_code=INVALID_PARAMETER_VALUE)
        elif len(parsed) > 1:
            raise MlflowException("Search filter contained multiple expression '%s'. "
                                  "Provide AND-ed expression list." % filter_string,
                                  error_code=INVALID_PARAMETER_VALUE)
        return SearchUtils._process_statement(parsed[0]) 

def _validate_order_by_and_generate_token(cls, order_by):
        try:
            parsed = sqlparse.parse(order_by)
        except Exception:
            raise MlflowException(f"Error on parsing order_by clause '{order_by}'",
                                  error_code=INVALID_PARAMETER_VALUE)
        if len(parsed) != 1 or not isinstance(parsed[0], Statement):
            raise MlflowException(f"Invalid order_by clause '{order_by}'. Could not be parsed.",
                                  error_code=INVALID_PARAMETER_VALUE)
        statement = parsed[0]
        if len(statement.tokens) == 1 and isinstance(statement[0], Identifier):
            token_value = statement.tokens[0].value
        elif len(statement.tokens) == 1 and \
                statement.tokens[0].match(ttype=TokenType.Keyword,
                                          values=[cls.ORDER_BY_KEY_TIMESTAMP]):
            token_value = cls.ORDER_BY_KEY_TIMESTAMP
        elif statement.tokens[0].match(ttype=TokenType.Keyword,
                                       values=[cls.ORDER_BY_KEY_TIMESTAMP])\
                and all([token.is_whitespace for token in statement.tokens[1:-1]])\
                and statement.tokens[-1].ttype == TokenType.Keyword.Order:
            token_value = cls.ORDER_BY_KEY_TIMESTAMP + ' ' + statement.tokens[-1].value
        else:
            raise MlflowException(f"Invalid order_by clause '{order_by}'. Could not be parsed.",
                                  error_code=INVALID_PARAMETER_VALUE)
        return token_value 

def process(self, stream):
        """Process the stream"""
        EOS_TTYPE = T.Whitespace, T.Comment.Single

        # Run over all stream tokens
        for ttype, value in stream:
            # Yield token if we finished a statement and there's no whitespaces
            # It will count newline token as a non whitespace. In this context
            # whitespace ignores newlines.
            # why don't multi line comments also count?
            if self.consume_ws and ttype not in EOS_TTYPE:
                yield sql.Statement(self.tokens)

                # Reset filter and prepare to process next statement
                self._reset()

            # Change current split level (increase, decrease or remain equal)
            self.level += self._change_splitlevel(ttype, value)

            # Append the token to the current statement
            self.tokens.append(sql.Token(ttype, value))

            # Check if we get the end of a statement
            if self.level <= 0 and ttype is T.Punctuation and value == ';':
                self.consume_ws = True

        # Yield pending statement (if any)
        if self.tokens:
            yield sql.Statement(self.tokens) 

def process(self, stack, stream):
        "Process the stream"
        consume_ws = False
        splitlevel = 0
        stmt = None
        stmt_tokens = []

        # Run over all stream tokens
        for ttype, value in stream:
            # Yield token if we finished a statement and there's no whitespaces
            if consume_ws and ttype not in (T.Whitespace, T.Comment.Single):
                stmt.tokens = stmt_tokens
                yield stmt

                # Reset filter and prepare to process next statement
                self._reset()
                consume_ws = False
                splitlevel = 0
                stmt = None

            # Create a new statement if we are not currently in one of them
            if stmt is None:
                stmt = Statement()
                stmt_tokens = []

            # Change current split level (increase, decrease or remain equal)
            splitlevel += self._change_splitlevel(ttype, value)

            # Append the token to the current statement
            stmt_tokens.append(Token(ttype, value))

            # Check if we get the end of a statement
            if splitlevel <= 0 and ttype is T.Punctuation and value == ';':
                consume_ws = True

        # Yield pending statement (if any)
        if stmt is not None:
            stmt.tokens = stmt_tokens
            yield stmt 

def test_issue9(self):
        # make sure where doesn't consume parenthesis
        p = sqlparse.parse('(where 1)')[0]
        self.assert_(isinstance(p, sql.Statement))
        self.assertEqual(len(p.tokens), 1)
        self.assert_(isinstance(p.tokens[0], sql.Parenthesis))
        prt = p.tokens[0]
        self.assertEqual(len(prt.tokens), 3)
        self.assertEqual(prt.tokens[0].ttype, T.Punctuation)
        self.assertEqual(prt.tokens[-1].ttype, T.Punctuation) 

def process(self, stack, stream):
        "Process the stream"
        consume_ws = False
        splitlevel = 0
        stmt = None
        stmt_tokens = []

        # Run over all stream tokens
        for ttype, value in stream:
            # Yield token if we finished a statement and there's no whitespaces
            if consume_ws and ttype not in (T.Whitespace, T.Comment.Single):
                stmt.tokens = stmt_tokens
                yield stmt

                # Reset filter and prepare to process next statement
                self._reset()
                consume_ws = False
                splitlevel = 0
                stmt = None

            # Create a new statement if we are not currently in one of them
            if stmt is None:
                stmt = Statement()
                stmt_tokens = []

            # Change current split level (increase, decrease or remain equal)
            splitlevel += self._change_splitlevel(ttype, value)

            # Append the token to the current statement
            stmt_tokens.append(Token(ttype, value))

            # Check if we get the end of a statement
            if splitlevel <= 0 and ttype is T.Punctuation and value == ';':
                consume_ws = True

        # Yield pending statement (if any)
        if stmt is not None:
            stmt.tokens = stmt_tokens
            yield stmt 

def _parse_filter_for_model_registry(cls, filter_string, valid_search_keys):
        if not filter_string or filter_string == "":
            return []
        expected = "Expected search filter with single comparison operator. e.g. name='myModelName'"
        try:
            parsed = sqlparse.parse(filter_string)
        except Exception:
            raise MlflowException("Error while parsing filter '%s'. %s" % (filter_string, expected),
                                  error_code=INVALID_PARAMETER_VALUE)
        if len(parsed) == 0 or not isinstance(parsed[0], Statement):
            raise MlflowException("Invalid filter '%s'. Could not be parsed. %s" %
                                  (filter_string, expected), error_code=INVALID_PARAMETER_VALUE)
        elif len(parsed) > 1:
            raise MlflowException("Search filter '%s' contains multiple expressions. "
                                  "%s " % (filter_string, expected),
                                  error_code=INVALID_PARAMETER_VALUE)
        statement = parsed[0]
        invalids = list(filter(cls._invalid_statement_token, statement.tokens))
        if len(invalids) > 0:
            invalid_clauses = ", ".join("'%s'" % token for token in invalids)
            raise MlflowException("Invalid clause(s) in filter string: %s. "
                                  "%s" % (invalid_clauses, expected),
                                  error_code=INVALID_PARAMETER_VALUE)
        return [cls._get_comparison_for_model_registry(
            si,
            valid_search_keys)
            for si in statement.tokens if isinstance(si, Comparison)] 

def __init__(self, statement: U[Statement, Token]):
        self._statement = statement
        self._tok_id = 0
        self._gen_inst = self._generator()