Support python3

[maxhutch]

Here's a bunch of "translation". Python2.7 seems to still be working fine. I've run into a non-trivial issue in Python3. I can authenticate, but issuing any real calls leads to an error buried in sockets. Any suggestions?

maxhutch@edoras:~/src/transfer-api-client-python$ ~/anaconda3/bin/python -i -m globusonline.transfer.api_client.main maxhutch -p
Globus Online Password: 
>>> api.task_list()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/maxhutch/src/transfer-api-client-python/globusonline/transfer/api_client/__init__.py", line 387, in task_list
    return self.get("/task_list" + encode_qs(kw))
  File "/home/maxhutch/src/transfer-api-client-python/globusonline/transfer/api_client/__init__.py", line 347, in get
    return self._request_json("GET", path)
  File "/home/maxhutch/src/transfer-api-client-python/globusonline/transfer/api_client/__init__.py", line 323, in _request_json
    r, response_body = self._request(method, path, body, content_type)
  File "/home/maxhutch/src/transfer-api-client-python/globusonline/transfer/api_client/__init__.py", line 267, in _request
    r, response_body = do_request()
  File "/home/maxhutch/src/transfer-api-client-python/globusonline/transfer/api_client/__init__.py", line 258, in do_request
    self.c.request(method, url, body=body, headers=headers)
  File "/home/maxhutch/anaconda3/lib/python3.4/http/client.py", line 1090, in request
    self._send_request(method, url, body, headers)
  File "/home/maxhutch/anaconda3/lib/python3.4/http/client.py", line 1128, in _send_request
    self.endheaders(body)
  File "/home/maxhutch/anaconda3/lib/python3.4/http/client.py", line 1086, in endheaders
    self._send_output(message_body)
  File "/home/maxhutch/anaconda3/lib/python3.4/http/client.py", line 924, in _send_output
    self.send(msg)
  File "/home/maxhutch/anaconda3/lib/python3.4/http/client.py", line 859, in send
    self.connect()
  File "/home/maxhutch/src/transfer-api-client-python/globusonline/transfer/api_client/verified_https.py", line 97, in connect
    sock = socket.create_connection((self.host, self.port), self.timeout)
  File "/home/maxhutch/anaconda3/lib/python3.4/socket.py", line 509, in create_connection
    raise err
  File "/home/maxhutch/anaconda3/lib/python3.4/socket.py", line 500, in create_connection
    sock.connect(sa)
BlockingIOError: [Errno 115] Operation now in progress

[bd4]

The verified_https code relies on internals (non-public api) which probably changed in 3.x. It looks like 3.4 has better built-in support for verifying peer certificates, but not sure about earlier 3.x. It will probably be a pain to make verified _https support a wider range of versions, but not impossible. This is one of the biggest failings of the Python standard library, we shouldn't have to go through major hoops just to get not broken https, I can't believe it took until 3.4.

Another direction would be to use a third party library like requests, but I really want Transfer API lib to work out of the box with Python standard lib.

[bd4]

Before spending time on verified_https, I would sub the standard lib HTTPSConnection back in(don't use verified_https at all) and see if it works in Python3. My guess is that it will work and the problem really is in verified_https, but it's possible there is a more subtle change in how the httplib works that is causing it to break.