I want to use generator yield and async functions. I read this topic, and wrote next code:
import asyncio
async def createGenerator():
mylist = range(3)
for i in mylist:
await asyncio.sleep(1)
yield i*i
async def start():
mygenerator = await createGenerator()
for i in mygenerator:
print(i)
loop = asyncio.get_event_loop()
try:
loop.run_until_complete(start())
except KeyboardInterrupt:
loop.stop()
pass
But i got the error:
SyntaxError: 'yield' inside async function
How to use yield generator in async function?
Upd:
Starting with Python 3.6 we have asynchronous generators and able to use yield directly inside coroutines.
import asyncio
async def async_generator():
for i in range(3):
await asyncio.sleep(1)
yield i*i
async def main():
async for i in async_generator():
print(i)
loop = asyncio.get_event_loop()
try:
loop.run_until_complete(main())
finally:
loop.run_until_complete(loop.shutdown_asyncgens()) # see: https://docs.python.org/3/library/asyncio-eventloop.html#asyncio.loop.shutdown_asyncgens
loop.close()
Old answer for Python 3.5:
You can't yield inside coroutines. Only way is to implement Asynchronous Iterator manually using __aiter__/__anext__ magic methods. In your case:
import asyncio
class async_generator:
def __init__(self, stop):
self.i = 0
self.stop = stop
async def __aiter__(self):
return self
async def __anext__(self):
i = self.i
self.i += 1
if self.i <= self.stop:
await asyncio.sleep(1)
return i * i
else:
raise StopAsyncIteration
async def main():
async for i in async_generator(3):
print(i)
if __name__ == "__main__":
loop = asyncio.get_event_loop()
loop.run_until_complete(main())
Output:
0
1
4