I think something like this should be in the standard library.
While yes, running a coroutine in a new task is in the standard library, that is only a component of what this library does, which is:
- given an async iterable,
- iterating over it in a new task, into a buffer,
- and then returning an iterable that yields values from this buffer as it's filled.
I don't _think_ this logic is in the standard library, at least not at https://docs.python.org/3/library/asyncio-task.html#asyncio.... from what I can see.
Have you thought about making it work as a decorator?
The issue is what happens on exceptions to avoid tasks hanging around forever. Exceptions propagate “forward” in the pipeline fairly automatically. However, getting the ones “behind” the exception to notice: that was tricky. The best I came up with was the bit of state wrapped up in buffered_pipeline that notices the exceptions and cancels the tasks.
I've gotten along ok with create_task and gather. I'll need to spend some time with this implementation to see if it fits any of my existing asyncio coding patterns.
An eagerly executing coroutine to consume the original generator and put it in a queue, and a new simple generator that yields values from the queue till it's told to stop.
I'm not sure if this matches the behavior of the original library for task cancellation though.
def eager_gen(gen):
end_marker = object()
queue = asyncio.Queue()
async def consumer():
try:
async for val in gen:
await queue.put(val)
except Exception as e:
await queue.put((end_marker, e))
else:
await queue.put((end_marker, None))
async def new_gen():
while True:
item = await queue.get()
if isinstance(item, tuple) and item[0] == end_marker:
break
yield item
if item[1]:
raise item[1] from None
_task = asyncio.create_task(consumer())
return new_gen()