Get address of a POST request to the service.

def _request_address(self):
        """Get address of a POST request to the service."""
        if not self._request_address_val:
            template = (
                'https://sb-ssl.google.com/safebrowsing/api/lookup'
                '?client={0}&key={1}&appver={2}&pver={3}'
            )
            self._request_address_val = template.format(
                self.client_name,
                self.api_key,
                self.app_version,
                self.protocol_version
            )
        return self._request_address_val