# Buggy code
def start_download():
    def cb(ds):
        logger.info(
            "Download infohash=%s, down=%s, progress=%s, status=%s, seedpeers=%s, candidates=%d"
            % (
                tdef.get_infohash().encode("hex")[:10],
                ds.get_current_speed("down"),
                ds.get_progress(),
                dlstatus_strings[ds.get_status()],
                sum(ds.get_num_seeds_peers()),
                sum(
                    1
                    for _ in anon_tunnel.community.dispersy_yield_verified_candidates()
                ),
            )
        )
        return 1.0, False

    download = anon_tunnel.session.start_download_from_tdef(tdef, dscfg)
    download.set_state_callback(cb, delay=1)


# Traceback (isError)
Regression

Tribler.Test.Core.Modules.RestApi.test_downloads_endpoint.TestDownloadsEndpoint.test_remove_download_no_remove_data_param (from nosetests)
Failing for the past 1 build (Since Failed#2109 )
Took 4.4 sec.
Error Message

Test raised 1 unhandled Twisted exceptions:
[{'log_namespace': u'log_legacy', 'log_time': 1467938979.639, 'format': '%(log_legacy)s', 'log_system': '-', 'log_legacy': <twisted.logger._stdlib.StringifiableFromEvent object at 0x06D22830>, 'log_level': <LogLevel=critical>, 'system': '-', 'isError': 1, 'failure': <twisted.python.failure.Failure exceptions.AttributeError: 'NoneType' object has no attribute 'add_task'>, 'time': 1467938979.639, 'log_text': 'Unhandled Error\nTraceback (most recent call last):\n  File "C:\\Python27\\lib\\threading.py", line 763, in run\n    self.__target(*self.__args, **self.__kwargs)\n  File "C:\\workspace\\jenkins\\workspace\\GH_Tribler_PR_tests_win32\\tribler\\Tribler\\Core\\Utilities\\twisted_thread.py", line 55, in _reactor_runner\n    reactor.run(installSignalHandlers=False)\n  File "C:\\Python27\\lib\\site-packages\\twisted\\internet\\base.py", line 1194, in run\n    self.mainLoop()\n  File "C:\\Python27\\lib\\site-packages\\twisted\\internet\\base.py", line 1203, in mainLoop\n    self.runUntilCurrent()\n--- <exception caught here> ---\n  File "C:\\Python27\\lib\\site-packages\\twisted\\internet\\base.py", line 825, in runUntilCurrent\n    call.func(*call.args, **call.kw)\n  File "C:\\workspace\\jenkins\\workspace\\GH_Tribler_PR_tests_win32\\tribler\\Tribler\\Core\\Libtorrent\\__init__.py", line 27, in <lambda>\n    lambda_f = lambda a = args, kwa = kwargs: invoke_func(*a, **kwa)\n  File "C:\\workspace\\jenkins\\workspace\\GH_Tribler_PR_tests_win32\\tribler\\Tribler\\Core\\Libtorrent\\__init__.py", line 28, in invoke_func\n    download.session.lm.threadpool.add_task(lambda_f, 1)\nexceptions.AttributeError: \'NoneType\' object has no attribute \'add_task\'\n', 'log_format': u'{log_text}', 'message': (), 'why': None}]

# Fixed code
def start_download():
    def cb(ds):
        logger.info(
            "Download infohash=%s, down=%s, progress=%s, status=%s, seedpeers=%s, candidates=%d"
            % (
                tdef.get_infohash().encode("hex")[:10],
                ds.get_current_speed("down"),
                ds.get_progress(),
                dlstatus_strings[ds.get_status()],
                sum(ds.get_num_seeds_peers()),
                sum(
                    1
                    for _ in anon_tunnel.community.dispersy_yield_verified_candidates()
                ),
            )
        )
        return 1.0, False

    download = anon_tunnel.session.start_download_from_tdef(tdef, dscfg)
    download.set_state_callback(cb)