python - 在 block 中持久化和获取数据

Question

我有一种情况 - 我在 Python 3.x 中使用 asyncio 包，并将数据保存在 with block 中，如下所示:

test_repo = TestRepository()

with (yield from test_repo):
    res = yield from test_repo.get_by_lim_off(
            page_size=int(length),
            offset=start,
            customer_name=customer_name,
            customer_phone=customer_phone,
            return_type=return_type
        )

我需要在 with block 中获取 res 数据，但是当我从 with block 退出时应该发生持久性和获取数据。我怎样才能做到这一点？

Answer 1

此行为仅在 Python 3.5+ 中受支持，通过异步上下文管理器(__aenter__/__aexit__)和async with，两者在 PEP 492 中添加:

class TestRepository:
   # All your normal methods go here

   async def __aenter__(self):
      # You can call coroutines here
      await self.some_init()

   async def __aexit__(self, exc_type, exc, tb):
      # You can call coroutines here
      await self.do_persistence()
      await self.fetch_data()


async def do_work():
    test_repo = TestRepository()

    async with test_repo:
        res = await test_repo.get_by_lim_off(
                page_size=int(length),
                offset=start,
                customer_name=customer_name,
                customer_phone=customer_phone,
                return_type=return_type
            )

 asyncio.get_event_loop().run_until_complete(do_work())

在 3.5 之前，您必须使用 try/finally block 显式调用 init/cleanup 协程，不幸的是:

@asyncio.coroutine
def do_work():
    test_repo = TestRepository()

    yield from test_repo.some_init()
    try:
        res = yield from test_repo.get_by_lim_off(
                page_size=int(length),
                offset=start,
                customer_name=customer_name,
                customer_phone=customer_phone,
                return_type=return_type
            )
    finally:
        yield from test_repo.do_persistence()
        yield from test_repo.fetch_data()