code: def _get_arn_from_idempotency_token(self, token):
          
          now = datetime.datetime.now()
          if token in self._idempotency_tokens:
              if self._idempotency_tokens[token]['expires'] < now:
                  # Token has expired, new request
                  del self._idempotency_tokens[token]
                  return None
              else:
                  return self._idempotency_tokens[token]['arn']
  
          return None
docs: If token doesnt exist, return None, later it will be
          set with an expiry and arn.
  
          If token expiry has passed, delete entry and return None
  
          Else return ARN
  
          :param token: String token
          :return: None or ARN