Sample aiohttp handler

user.py

@routes.get("/user/{username}")
async def get_user(request: web.Request):
   username = request.match_info.get("username")
   if username not in USER_DB:
       return web.json_response(
           data={"message": "User not found"},
           status=404
       )
   return web.json_response(data=USER_DB.get(username))