來自Python 3的TypeError異步循環

Question

我正在學習Python的相對較新的異步功能。我發現這在PEP 492：

The following is a utility class that transforms a regular iterable to an asynchronous one. While this is not a very useful thing to do, the code illustrates the relationship between regular and asynchronous iterators.

class AsyncIteratorWrapper: 
    def __init__(self, obj): 
     self._it = iter(obj) 

    def __aiter__(self): 
     return self 

    async def __anext__(self): 
     try: 
      value = next(self._it) 
     except StopIteration: 
      raise StopAsyncIteration 
     return value 

async for letter in AsyncIteratorWrapper("abc"): 
    print(letter) 

我試圖通過增加給定async for循環的功能，然後調用，使用一個事件循環運行該代碼。

完整的示例代碼（在解釋器中運行）：

class AsyncIteratorWrapper: 
    def __init__(self, obj): 
     self._it = iter(obj) 
    def __aiter__(self): 
     return self 
    async def __anext__(self): 
     try: 
      value = next(self._it) 
     except StopIteration: 
      raise StopAsyncIteration 
     return value 

async def aprint(str): 
    async for letter in AsyncIteratorWrapper(str): 
    print(letter) 

import asyncio 
loop = asyncio.get_event_loop() 
co = aprint("abcde") 
loop.run_until_complete(co) 

不過，我得到一個錯誤：

Traceback (most recent call last): 
    File "<stdin>", line 1, in <module> 
    File "/opt/rh/rh-python35/root/usr/lib64/python3.5/asyncio/base_events.py", line 337, in run_until_complete 
    return future.result() 
    File "/opt/rh/rh-python35/root/usr/lib64/python3.5/asyncio/futures.py", line 274, in result 
    raise self._exception 
    File "/opt/rh/rh-python35/root/usr/lib64/python3.5/asyncio/tasks.py", line 239, in _step 
    result = coro.send(None) 
    File "<stdin>", line 2, in aprint 
TypeError: 'async for' received an invalid object from __aiter__: AsyncIteratorWrapper 

我在做什麼錯？這個例子如何解決？我感到有點驚訝，PEP中的代碼失敗了。

我正在使用python版本3.5.1。

Answer 1

您使用的代碼適用於python 3.5.2+。

從Python 3.5.2 __aiter__可以直接返回異步迭代器。 More here

您收到的錯誤是由於較舊的python（3.5.1），因此它返回了錯誤的類型。