Since 3.5.2 sock_connect() tries to be smart and resolves addresses for you if they fail a socket.inet_pton() check. But inet_pton() only supports AF_INET(6) and does not work for other address families that socket otherwise supports just fine (e.g. AF_BLUETOOTH).

Before 3.5.2, in order to happily use bluetooth sockets with asyncio, you could just do:

    sock = socket.socket(family=socket.AF_BLUETOOTH, type=socket.SOCK_STREAM,
                proto=socket.BTPROTO_RFCOMM)
    sock.setblocking(False)
    addr = "00:12:34:56:78:99"
    yield from loop.sock_connect(sock, (addr, 1))

This is a regression.

The error for inet_pton() is:

>>> import socket
>>> socket.inet_pton(socket.AF_BLUETOOTH, "00:12:34:56:78:99")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
socket.error: [Errno 97] Address family not supported by protocol

And the traceback in asyncio is:

DEBUG:asyncio:Using selector: EpollSelector
Traceback (most recent call last):
  File "log.py", line 91, in <module>
    main()
  File "log.py", line 84, in main
    loop.run_until_complete(log(loop, sys.argv[1]))
  File "/usr/lib/python3.5/asyncio/base_events.py", line 387, in run_until_complete
    return future.result()
  File "/usr/lib/python3.5/asyncio/futures.py", line 274, in result
    raise self._exception
  File "/usr/lib/python3.5/asyncio/tasks.py", line 241, in _step
    result = coro.throw(exc)
  File "log.py", line 22, in log
    yield from loop.sock_connect(sock, (addr, 1))
  File "/usr/lib/python3.5/asyncio/selector_events.py", line 397, in sock_connect
    yield from resolved
  File "/usr/lib/python3.5/asyncio/futures.py", line 361, in __iter__
    yield self  # This tells Task to wait for completion.
  File "/usr/lib/python3.5/asyncio/tasks.py", line 296, in _wakeup
    future.result()
  File "/usr/lib/python3.5/asyncio/futures.py", line 274, in result
    raise self._exception
  File "/usr/lib/python3.5/concurrent/futures/thread.py", line 55, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/usr/lib/python3.5/socket.py", line 732, in getaddrinfo
    for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
socket.gaierror: [Errno -5] No address associated with hostname

Thanks for the report! I'm unable to reproduce, as `socket.AF_BLUETOOTH` doesn't exist on my system, but surely someone else can.

Looks related (possibly a duplicate) of issue #27136. Also related is a fix for the latter in https://github.com/python/asyncio/pull/357. That fix is already in the CPython repo, but I guess it didn't make it into 3.5.2.

https://github.com/python/cpython/blob/master/Lib/asyncio/selector_events.py#L394
https://github.com/python/asyncio/blob/master/asyncio/selector_events.py#L394

AF_UNIX is special-cased.
Maybe AF_BLUETOOTH and others should use that same special treatment.
Or maybe only AF_INET, AF_INET6 should attempt resolving.

I'm not sure this is still relevant for the latest asyncio in 3.6.  Robert, could you please test if this is still the case?

It is still in cpython master e6e9ddd.

import asyncio
import socket
sock = socket.socket(family=socket.AF_BLUETOOTH,
                     type=socket.SOCK_STREAM,
                     proto=socket.BTPROTO_RFCOMM)
sock.setblocking(False)
addr = "00:12:34:56:78:99"
loop = asyncio.get_event_loop()
loop.run_until_complete(loop.sock_connect(sock, (addr, 1)))

Traceback (most recent call last):
  File "/home/rj/work/hxm/t.py", line 9, in <module>
    loop.run_until_complete(loop.sock_connect(sock, (addr, 1)))
  File "/home/rj/src/cpython/Lib/asyncio/base_events.py", line 457, in run_until_complete
    return future.result()
  File "/home/rj/src/cpython/Lib/asyncio/futures.py", line 292, in result
    raise self._exception
  File "/home/rj/src/cpython/Lib/asyncio/tasks.py", line 241, in _step
    result = coro.throw(exc)
  File "/home/rj/src/cpython/Lib/asyncio/selector_events.py", line 416, in sock_connect
    yield from resolved
  File "/home/rj/src/cpython/Lib/asyncio/futures.py", line 379, in __iter__
    yield self  # This tells Task to wait for completion.
  File "/home/rj/src/cpython/Lib/asyncio/tasks.py", line 297, in _wakeup
    future.result()
  File "/home/rj/src/cpython/Lib/asyncio/futures.py", line 292, in result
    raise self._exception
  File "/home/rj/src/cpython/Lib/concurrent/futures/thread.py", line 55, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/home/rj/src/cpython/Lib/socket.py", line 743, in getaddrinfo
    for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
socket.gaierror: [Errno -6] ai_family not supported

New changeset 5c30388f3c586ba2f33e349e22e5949cb92de621 by Vincent Bernat in branch 'main':
bpo-27929: resolve names only for AF_INET/AF_INET6 with asyncio (GH-32131)
https://github.com/python/cpython/commit/5c30388f3c586ba2f33e349e22e5949cb92de621

New changeset 2bcbc3113dee6c35631595ec0d5ee3a8dd2a2ddd by Miss Islington (bot) in branch '3.10':
bpo-27929: resolve names only for AF_INET/AF_INET6 with asyncio (GH-32131)
https://github.com/python/cpython/commit/2bcbc3113dee6c35631595ec0d5ee3a8dd2a2ddd

New changeset f84fb55659079bbc99d4cd0441dc13ab07ac3dcf by Miss Islington (bot) in branch '3.9':
bpo-27929: resolve names only for AF_INET/AF_INET6 with asyncio (GH-32131)
https://github.com/python/cpython/commit/f84fb55659079bbc99d4cd0441dc13ab07ac3dcf