Why asyncio Queue is behaving so weirdly here, even though putting an item there it is showing empty?
In [1]: from multiprocessing import Queue
In [2]: q = Queue()
In [3]: q.empty()
Out[3]: True
In [4]: q.put(100)
In [5]: q.empty()
Out[5]: False
In [6]: from asyncio import Queue
In [7]: q = Queue()
In [8]: q.empty()
Out[8]: True
In [9]: q.put(100)
Out[9]: <generator object Queue.put at 0x7f97849bafc0>
In [10]: q.empty()
Out[10]: True
Because you didn't put anything:
q.put(100)
put here - is not a plain function, it's a coroutine. You should await it to put item in queue.
For example:
import asyncio
from asyncio import Queue
async def main():
q = Queue()
print(q.empty()) # True
await q.put(100)
print(q.empty()) # False
if __name__ == '__main__':
loop = asyncio.get_event_loop()
try:
loop.run_until_complete(main())
finally:
loop.run_until_complete(loop.shutdown_asyncgens())
loop.close()
As Mikhail Gerasimov's answer, q.put(100) is a coroutine and explaining more detail...
Calling a coroutine does not start its code running – the coroutine object returned by the call doesn’t do anything until you schedule its execution. There are two basic ways to start it running: call await coroutine or yield from coroutine from another coroutine (assuming the other coroutine is already running!), or schedule its execution using the ensure_future() function or the AbstractEventLoop.create_task() method.
Coroutines (and tasks) can only run when the event loop is running.
It is from Python Coroutines doc.
In the Mikhail Gerasimov's example,
Another coroutine async def main() calls await with coroutine q.put(100) and event loop is running loop.run_until_complete(main()) such as the above description.
