<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 async def load_user(self, request):
 """Load user from request."""

        if USER_KEY not in request:
            session = await self.load(request)
            if 'id' not in session:
                return None

            request[USER_KEY] = request.user = await self._user_loader(session['id'])

        return request[USER_KEY]