I am seeing this error on Windows and Mac CI builds where FTP related tests in test.test_urllib2net.TimeoutTest are failing. It's reproducible locally too where the tests are skipped on Mac and Ubuntu. Not sure if it's random since several PRs in the last few hours fail with this.

Appveyor : 

* https://ci.appveyor.com/project/python/cpython/builds/22675425#L2817

VSTS builds : 

* https://dev.azure.com/Python/cpython/_build/results?buildId=38631
* https://dev.azure.com/Python/cpython/_build/results?buildId=38625

$ ./python.exe -m unittest -vv test.test_urllib2net.TimeoutTest
test_ftp_basic (test.test_urllib2net.TimeoutTest) ... skipped "Resource 'ftp://www.pythontest.net/' is not available"
test_ftp_default_timeout (test.test_urllib2net.TimeoutTest) ... skipped "Resource 'ftp://www.pythontest.net/' is not available"
test_ftp_no_timeout (test.test_urllib2net.TimeoutTest) ... /Users/karthikeyansingaravelan/stuff/python/cpython/Lib/encodings/idna.py:163: ResourceWarning: unclosed <socket.socket fd=7, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('192.168.3.111', 49633), raddr=('159.89.235.38', 21)>
  for label in labels[:-1]:
ResourceWarning: Enable tracemalloc to get the object allocation traceback
/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/encodings/idna.py:163: ResourceWarning: unclosed <socket.socket fd=8, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('192.168.3.111', 49635), raddr=('159.89.235.38', 21)>
  for label in labels[:-1]:
ResourceWarning: Enable tracemalloc to get the object allocation traceback
/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/encodings/idna.py:163: ResourceWarning: unclosed <socket.socket fd=10, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('192.168.3.111', 49639), raddr=('159.89.235.38', 21)>
  for label in labels[:-1]:
ResourceWarning: Enable tracemalloc to get the object allocation traceback
/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/encodings/idna.py:163: ResourceWarning: unclosed <socket.socket fd=11, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('192.168.3.111', 49641), raddr=('159.89.235.38', 21)>
  for label in labels[:-1]:
ResourceWarning: Enable tracemalloc to get the object allocation traceback
/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/encodings/idna.py:163: ResourceWarning: unclosed <socket.socket fd=12, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('192.168.3.111', 49643), raddr=('159.89.235.38', 21)>
  for label in labels[:-1]:
ResourceWarning: Enable tracemalloc to get the object allocation traceback
skipped "Resource 'ftp://www.pythontest.net/' is not available"
test_ftp_timeout (test.test_urllib2net.TimeoutTest) ... skipped "Resource 'ftp://www.pythontest.net/' is not available"
test_http_basic (test.test_urllib2net.TimeoutTest) ... ok
test_http_default_timeout (test.test_urllib2net.TimeoutTest) ... ok
test_http_no_timeout (test.test_urllib2net.TimeoutTest) ... ok
test_http_timeout (test.test_urllib2net.TimeoutTest) ... ok

----------------------------------------------------------------------
Ran 8 tests in 33.617s

OK (skipped=4)