import asyncio

class User:
    def __init__(self):
        self.id = None
        self.username = None

    @classmethod
    async def create(cls, id):
      user = cls()
      user.id = id
      user.username = await get_username(id)
      return user


async def main():
  user = await User.create(1)
  print(user.username)

async def get_username(id):
    await asyncio.sleep(1)
    return "shiro"

loop = asyncio.get_event_loop()
loop.run_until_complete(main())