<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def fetch_request_token(self, oauth_request):
 """Processes a request_token request and returns the request token on success. """

        try:
            # Get the request token for authorization.
            token = self._get_token(oauth_request, 'request')
        except Error:
            # No token required for the initial token request.
            version = self._get_version(oauth_request)
            consumer = self._get_consumer(oauth_request)
            try:
                callback = self.get_callback(oauth_request)
            except Error:
                callback = None # 1.0, no callback specified.
            self._check_signature(oauth_request, consumer, None)
            # Fetch a new token.
            token = self.data_store.fetch_request_token(consumer, callback)
        return token