在使用 Jupiter Notebook 时，“ syncio.run()不能从正在运行的事件循环中调用”

The asyncio.run() documentation says:

This function cannot be called when another asyncio event loop is running in the same thread.

In your case, jupyter (IPython ≥ 7.0) is already running an event loop:

You can now use async/await at the top level in the IPython terminal and in the notebook, it should — in most of the cases — “just work”. Update IPython to version 7+, IPykernel to version 5+, and you’re off to the races.

Therefore you don't need to start the event loop yourself and can instead call await main(url) directly, even if your code lies outside any asynchronous function.

Jupyter / IPython

async def main():
print(1)
    

await main()

Python (≥ 3.7) or older versions of IPython

import asyncio


async def main():
print(1)
    

asyncio.run(main())

In your code that would give:

url = ['url1', 'url2']
result = await main(url)


for text in result:
pass # text contains your html (text) response

Caution

There is a slight difference on how Jupyter uses the loop compared to IPython.

To add to cglacet's answer - if one wants to detect whether a loop is running and adjust automatically (ie run main() on the existing loop, otherwise asyncio.run()), here is a snippet that may prove useful:

# async def main():
#     ...


try:
loop = asyncio.get_running_loop()
except RuntimeError:  # 'RuntimeError: There is no current event loop...'
loop = None


if loop and loop.is_running():
print('Async event loop already running. Adding coroutine to the event loop.')
tsk = loop.create_task(main())
# ^-- https://docs.python.org/3/library/asyncio-task.html#task-object
# Optionally, a callback function can be executed when the coroutine completes
tsk.add_done_callback(
lambda t: print(f'Task done with result={t.result()}  << return val of main()'))
else:
print('Starting new event loop')
result = asyncio.run(main())

As cglacet mentioned that documentation says

This function cannot be called when another asyncio event loop is running in the same thread.

You can use another thread i.e -

class ResolveThread(threading.Thread):
def __init__(self,result1,fun,url):
self.result1= result1
self.fun = fun
self.url = url
threading.Thread.__init__(self)
def run(self):
result1[0] = asyncio.run(self.fun(self.url))




result1 = [None]
sp = ResolveThread(result1)
sp.start()
sp.join() # connect main thread
result = result1[0]

Combining the methods from Pankaj Sharma and Jean Monet, I wrote the following snippet that acts as asyncio.run (with slightly different syntax), but also works within a Jupyter notebook.

class RunThread(threading.Thread):
def __init__(self, func, args, kwargs):
self.func = func
self.args = args
self.kwargs = kwargs
self.result = None
super().__init__()


def run(self):
self.result = asyncio.run(self.func(*self.args, **self.kwargs))


def run_async(func, *args, **kwargs):
try:
loop = asyncio.get_running_loop()
except RuntimeError:
loop = None
if loop and loop.is_running():
thread = RunThread(func, args, kwargs)
thread.start()
thread.join()
return thread.result
else:
return asyncio.run(func(*args, **kwargs))

Usage:

async def test(name):
await asyncio.sleep(5)
return f"hello {name}"


run_async(test, "user")  # blocks for 5 seconds and returns "hello user"

Just use this:

https://github.com/erdewit/nest_asyncio

import nest_asyncio
nest_asyncio.apply()

I found the unsync package useful for writing code that behaves the same way in a Python script and the Jupyter REPL.

import asyncio
from unsync import unsync




@unsync
async def demo_async_fn():
await asyncio.sleep(0.1)
return "done!"


print(demo_async_fn().result())