here is my code:

import asyncio
from aiohttp import ClientSession


async def main():
    url = "https://stackoverflow.com/"

    async with ClientSession() as session:
        async with session.get(url) as resp:
            print(resp.status)

asyncio.run(main())

if I run it on my computer, everything works, but if I run it on pythonanywhere, I get this error:

Traceback (most recent call last):
  File "/home/0dminnimda/.local/lib/python3.8/site-packages/aiohttp/connector.py", line 936, in _wrap_create_connection
    return await self._loop.create_connection(*args, **kwargs)  # type: ignore  # noqa
  File "/usr/lib/python3.8/asyncio/base_events.py", line 1017, in create_connection
    raise exceptions[0]
  File "/usr/lib/python3.8/asyncio/base_events.py", line 1002, in create_connection
    sock = await self._connect_sock(
  File "/usr/lib/python3.8/asyncio/base_events.py", line 916, in _connect_sock
    await self.sock_connect(sock, address)
  File "/usr/lib/python3.8/asyncio/selector_events.py", line 485, in sock_connect
    return await fut
  File "/usr/lib/python3.8/asyncio/selector_events.py", line 517, in _sock_connect_cb
    raise OSError(err, f'Connect call failed {address}')
ConnectionRefusedError: [Errno 111] Connect call failed ('151.101.193.69', 443)
The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "test_c.py", line 39, in <module>
    asyncio.run(main())
  File "/usr/lib/python3.8/asyncio/runners.py", line 43, in run
    return loop.run_until_complete(main)
  File "/usr/lib/python3.8/asyncio/base_events.py", line 608, in run_until_complete
    return future.result()
  File "test_c.py", line 28, in main
    async with session.get(url, timeout=30) as resp:  # , headers=headers
  File "/home/0dminnimda/.local/lib/python3.8/site-packages/aiohttp/client.py", line 1012, in __aenter__
    self._resp = await self._coro
  File "/home/0dminnimda/.local/lib/python3.8/site-packages/aiohttp/client.py", line 480, in _request
    conn = await self._connector.connect(
  File "/home/0dminnimda/.local/lib/python3.8/site-packages/aiohttp/connector.py", line 523, in connect
    proto = await self._create_connection(req, traces, timeout)
  File "/home/0dminnimda/.local/lib/python3.8/site-packages/aiohttp/connector.py", line 858, in _create_connection
    _, proto = await self._create_direct_connection(
  File "/home/0dminnimda/.local/lib/python3.8/site-packages/aiohttp/connector.py", line 1004, in _create_direct_connection
    raise last_exc
  File "/home/0dminnimda/.local/lib/python3.8/site-packages/aiohttp/connector.py", line 980, in _create_direct_connection
    transp, proto = await self._wrap_create_connection(
  File "/home/0dminnimda/.local/lib/python3.8/site-packages/aiohttp/connector.py", line 943, in _wrap_create_connection
    raise client_error(req.connection_key, exc) from exc
aiohttp.client_exceptions.ClientConnectorError: Cannot connect to host stackoverflow.com:443 ssl:default [Connect call failed ('151.101.193.69', 443)]
Unclosed client session
client_session: <aiohttp.client.ClientSession object at 0x7f25a71d1a90>

aiohttp on hosting:

Name: aiohttp
Version: 3.6.2
Summary: Async http client/server framework (asyncio)
Home-page: https://github.com/aio-libs/aiohttp
Author: Nikolay Kim
Author-email: fafhrd91@gmail.com
License: Apache 2
Location: /home/0dminnimda/.local/lib/python3.8/site-packages
Requires: chardet, async-timeout, multidict, yarl, attrs
Required-by: 

aiohttp on my PC:

Name: aiohttp
Version: 3.6.2
Summary: Async http client/server framework (asyncio)
Home-page: https://github.com/aio-libs/aiohttp
Author: Nikolay Kim
Author-email: fafhrd91@gmail.com
License: Apache 2
Location: c:\users\asus\appdata\roaming\python\python38\site-packages
Requires: async-timeout, attrs, chardet, yarl, multidict
Required-by: 

I am at a loss that it is not so? I am running both files using python3.8.

I also tried other urls, they have the same problem

Do I need to add any more details?

first solution

Referring to the help from the forum, I added trust_env = True when creating the client and now everything works.

Explanation: Free accounts on PythonAnywhere must use a proxy to connect to the public internet, but aiohttp, by default, does not connect to a proxy accessible from an environment variable.

Link to aiohttp documentation (look for a parameter called "trust_env")

Here is the new code:

import asyncio
from aiohttp import ClientSession


async def main():
    url = "https://stackoverflow.com/"

    async with ClientSession(trust_env=True) as session:
        async with session.get(url) as resp:
            print(resp.status)

asyncio.run(main())

solution if the first didn't help you

The domain you are trying to access must be in whitelist, otherwise you may also get this error.

In this case you need to post a new topic on the pythonanywhere forum asking to add the domain to the whitelist.
If this is an api, then you will need to provide a link to the documentation for this api.