"RuntimeError: no running event loop" with "asyncio.get_running_loop()" in Python

Question

I'm trying to run the code below with asyncio.get_running_loop():

import asyncio

async def test():
    for _ in range(3):
        print("Test")
        await asyncio.sleep(1)

loop = asyncio.get_running_loop() # Here

loop.run_until_complete(test()) 

But, I got the error below:

RuntimeError: no running event loop

I could run the code above by replacing asyncio.get_running_loop() with asyncio.get_event_loop() as shown below but asyncio.get_event_loop() is deprecated since version 3.10 so I don't want to use it.

# ...

loop = asyncio.get_event_loop() # Here
# loop = asyncio.get_running_loop()

# ...

So, this is the result below:

Test
Test
Test

So, how can I run the code above with asyncio.get_running_loop()?

Answer 1

You got the error because asyncio.get_running_loop() tried to get a running event loop but there is no running event loop to get:

asyncio.get_running_loop():

Return the running event loop in the current OS thread.

If there is no running event loop a RuntimeError is raised. This function can only be called from a coroutine or a callback.

So, you need to create and set an event loop with asyncio.new_event_loop() and asyncio.set_event_loop() instead of using asyncio.get_running_loop() as shown below:

import asyncio

async def test():
    for _ in range(3):
        print("Test")
        await asyncio.sleep(1)

loop = asyncio.new_event_loop() # Here
asyncio.set_event_loop(loop) # Here

# loop = asyncio.get_running_loop()

loop.run_until_complete(test()) 

Then, your code works properly:

Test
Test
Test

In addition, you can use asyncio.get_running_loop() like below. In this case, there is a running event loop and asyncio.get_running_loop() gets it so the error doesn't occur:

import asyncio

async def test():
    for _ in range(3):
        print("Test")
        await asyncio.sleep(1)

async def call_test():
    loop = asyncio.get_running_loop() # Here
    await loop.create_task(test())

loop = asyncio.new_event_loop()
asyncio.set_event_loop(loop)

loop.run_until_complete(call_test())  

Then, this code works properly as well:

Test
Test
Test