def write_identifier(self, identifier):
        """ Write an identifier.

        :arg identifier:
        """
        if not identifier:
            raise ValueError("Invalid identifier")
        identifier = ustr(identifier)
        safe = (self.safe_first_chars in identifier[0] and
                all(ch in self.safe_chars for ch in identifier[1:]))
        if not safe:
            self.file.write(u"`")
            self.file.write(identifier.replace(u"`", u"``"))
            self.file.write(u"`")
        else:
            self.file.write(identifier)
dataset/ETHPy150Open nigelsmall/py2neo/py2neo/database/cypher.py/CypherWriter.write_identifier/swapped operands of `in`