Unable to schedule anything in asyncio. (Python 3.7.x)

Question

I am currently working on asyncio with python 3.7.x not sure about the exact version, right now I am trying to schedule a task. And I am unable to get an output, even when running the thing forever. Here is the code I currently have

import asyncio

async def print_now():
  print("Hi there")

loop = asyncio.get_event_loop()
loop.call_later(print_now())
loop.run_until_complete(asyncio.sleep(1))

This gives the following error:

Traceback (most recent call last):
  File "D:\Coding\python\async\main.py", line 7, in <module>
    loop.call_later(print_now())
TypeError: call_later() missing 1 required positional argument: 'callback'

The call back in call_later() is print_now I've tried just print_now and print_now() I have also tried using loop.run_forever() instead of loop.run_until_complete() and so far I didn't get anything

Sometimes I get either no output or a different error.

Answer 1

First, yes, you're missing a delay argument . First one is supposed to be the delay while the second one is a callback ( docs ).

loop.call_later(delay, callback, *args, context=None)

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Second, the callback is supposed to be a function. What you're passing is print_now() which is gonna evaluate to None . You might find out that

'NoneType' object is not callable

So you're gonna need to pass print_now — without parentheses — as a callback. This way you're passing a function instead of the result of its application.

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Third, async functions are supposed to be await ed on. Your scenario doesn't seem to need that, so just drop the async keyword.

When you call an awaitable function, you create a new coroutine object. The code inside the function won't run until you then await on the function or run it as a task

From this post . You might want to check out