I'm trying on FC24, using python-ovirt-engine-sdk4-4.1.0-0.0.20161003git056315d.fc24.x86_64 to add a DC, and failing - against master. The client is unhappy:
File "/home/ykaul/ovirt-system-tests/basic-suite-master/test-scenarios/002_bootstrap.py", line 98, in add_dc4
    version=sdk4.types.Version(major=DC_VER_MAJ,minor=DC_VER_MIN),
  File "/usr/lib64/python2.7/site-packages/ovirtsdk4/services.py", line 4347, in add
    response = self._connection.send(request)
  File "/usr/lib64/python2.7/site-packages/ovirtsdk4/__init__.py", line 276, in send
    return self.__send(request)
  File "/usr/lib64/python2.7/site-packages/ovirtsdk4/__init__.py", line 298, in __send
    self._sso_token = self._get_access_token()
  File "/usr/lib64/python2.7/site-packages/ovirtsdk4/__init__.py", line 460, in _get_access_token
    sso_response = self._get_sso_response(self._sso_url, post_data)
  File "/usr/lib64/python2.7/site-packages/ovirtsdk4/__init__.py", line 498, in _get_sso_response
    return json.loads(body_buf.getvalue().decode('utf-8'))
  File "/usr/lib64/python2.7/json/__init__.py", line 339, in loads
    return _default_decoder.decode(s)
  File "/usr/lib64/python2.7/json/decoder.py", line 364, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib64/python2.7/json/decoder.py", line 382, in raw_decode
    raise ValueError("No JSON object could be decoded")
ValueError: No JSON object could be decoded


Surprisingly, I now can't find that RPM of this SDK in resources.ovirt.org now.

I've tried with http://resources.ovirt.org/pub/ovirt-master-snapshot/rpm/fc24/x86_64/python-ovirt-engine-sdk4-4.0.0-0.1.20161004gitf94eeb5.fc24.x86_64.rpm 

- same result.

Did not see anything obvious on server or engine logs.
The code:
def add_dc4(api):
    nt.assert_true(api != None)
    dcs_service = api.system_service().data_centers_service()
    nt.assert_true(
        dc = dcs_service.add(
            sdk4.types.DataCenter(
                name=DC_NAME4,
                description='APIv4 DC',
                local=False,
                version=sdk4.types.Version(major=DC_VER_MAJ,minor=DC_VER_MIN),
            ),
        )
    )


And the api object is from:
            return sdk4.Connection(
                url=url,
                username=constants.ENGINE_USER,
                password=str(self.metadata['ovirt-engine-password']),
                insecure=True,
                debug=True,
            )