[FIXED] Event loop exception after program finishes

Issue

W.r.t. Łukasz' tutorial on Youtube for a simple web-crawler, the following code gives RuntimeError: Event loop is closed. This happens after the code runs successfully and prints out the time taken to complete the program.

import asyncio
import time
from typing import Callable, Coroutine
import httpx

addr = 'https://langa.pl/crawl'


async def progress(
    url: str,
    algo: Callable[..., Coroutine],
) -> None:

    # store create_task into a variable
    task = asyncio.create_task(
        algo(url),
        name=url,
    )

    todo.add(task)  # add task to todo
    start = time.time()

    while len(todo):

        done, _pending = await asyncio.wait(todo, timeout=0.5)

        # cleanup todo by removing the done task
        todo.difference_update(done)

        # report completed urls
        urls = (t.get_name() for t in todo)

        # prints the current status
        print(f"{len(todo)}: " + " ".join(sorted(urls))[-75:])

    end = time.time()
    print(f"Took {int(end-start)} seconds")


async def crawl3(
    prefix: str, url: str = "",
) -> None:
    url = url or prefix
    client = httpx.AsyncClient()
    try:
        res = await client.get(url)
    finally:
        await client.aclose()

    for line in res.text.splitlines():
        if line.startswith(prefix):
            task = asyncio.create_task(
                crawl3(prefix, line),
                name=line,
            )

            todo.add(task)

todo = set()
asyncio.run(progress(addr, crawl3))

Why is this happening? What needs to be changed in the code?

Solution

Resolved from pointer given by @user4815162342 - being tracked in this issue

import asyncio

import sys ## added to prevent Event Loop exception

import time
from typing import Callable, Coroutine

import httpx

## added to prevent Event Loop exception...
if sys.version_info[0] == 3 and sys.version_info[1] >= 8 and sys.platform.startswith('win'):
    asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())

addr = 'https://langa.pl/crawl'
...

Answered By - reservoirinvest