<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def refresh(self):
 """Obtain a new access token."""

        grant_type = "https://oauth.reddit.com/grants/installed_client"
        self._request_token(grant_type=grant_type, device_id=self._device_id)