How do I run a coroutine, and what do I need before I can?

How do I run a coroutine, and what do I need before I can?

To run a coroutine, you can use one of these mechanisms:
- Use asyncio.run(coro) to execute the coroutine in a new event loop and return its result. The argument can be any awaitable object. This function should be used as the main entry point for asyncio programs and cannot be called when another event loop is running in the same thread [2], "Running an asyncio Program".
- Await the coroutine from within another coroutine using the await keyword [1], "Coroutines".
- Use asyncio.create_task(coro) to schedule the coroutine as a Task for concurrent execution within an event loop. You must have a running event loop in the current thread, or a RuntimeError is raised [1], "Creating tasks".
- Use asyncio.TaskGroup (Python 3.11+) as an async context manager to create and manage multiple tasks [1], "Task groups".

Before you can run a coroutine:
- You need an event loop running in the current thread. asyncio.run() and asyncio.Runner() will create and manage the event loop for you. If you use create_task(), you must already be inside a running event loop (e.g., inside another coroutine) [1], "Creating tasks"; [2], "Running an asyncio Program".
- If you use asyncio.run(), you cannot already have another event loop running in the same thread [2], "Running an asyncio Program".

Example using asyncio.run():
```python
import asyncio

async def main():
    print('hello')
    await asyncio.sleep(1)
    print('world')

asyncio.run(main())
```
[1], "Coroutines"; [2], "Running an asyncio Program"

Example using create_task() inside a coroutine:
```python
import asyncio

async def say_after(delay, what):
    await asyncio.sleep(delay)
    print(what)

async def main():
    task1 = asyncio.create_task(say_after(1, 'hello'))
    task2 = asyncio.create_task(say_after(2, 'world'))
    await task1
    await task2

asyncio.run(main())
```
[1], "Coroutines"

Summary:
- Use asyncio.run() or asyncio.Runner().run() for top-level entry.
- Use await or create_task() inside a running event loop.
- You need a running event loop, which asyncio.run() provides, or you must already be inside one for create_task().
[1], "Coroutines", "Creating tasks"; [2], "Running an asyncio Program", "Runner context manager"

Sources
  [1] Coroutines and tasks  https://docs.python.org/3/library/asyncio-task.html
  [2] Runners  https://docs.python.org/3/library/asyncio-runner.html