Search string in JSON values without the key

Is it possible to search through a JSON and find a single string? I just want to know if this sting is in the JSON or not.

What I have tried before:

def parse_string(self, reg_string,  input_data):
        self.logger.info("parse string")
        for i in input_data:
            self.logger.info(input_data[i])
            if input_data[i] == reg_string:
                return (input_data[i])
            else:
                self.logger.info('regex: %s not found', reg_string)

but it prints lots of Nones.

My JSON:

{
  "id": 5931,
  "state": "opened",
  "created_at": "2020-09-24T15:04:05.728+02:00",
  "author": {
    "id": 130,
    "username": "veeti",
    "state": "active"
  }

How I call the method:

parser.parse_string("veeti", parser.data)

Answer

You could do str(json_value).find("veeti") > -1