def is_valid(self, node, lint_context):
        """ Whether the specified node is valid.

        In this policy, valid node is only 2 cases;
        - single quoted
        - double quoted, but including a special char

        See `:help expr-string`. """

        value = node['value']

        is_double_quoted = value[0] == '"'
        if not is_double_quoted:
            return True

        has_escaped_char = _special_char_matcher.search(value) != None
        return has_escaped_char
dataset/ETHPy150Open Kuniwak/vint/vint/linting/policy/prohibit_unnecessary_double_quote.py/ProhibitUnnecessaryDoubleQuote.is_valid/operator `is not` -> `!=`