I'm not familiar with this test.
Me neither, but Brett C should be. :-)
In a debug build:
""" C:\Code\python\PCbuild>python_d ../lib/test/test_urllibnet.py testURLread (__main__.URLTimeoutTest) ... ok test_bad_address (__main__.urlopenNetworkTests) ... ok test_basic (__main__.urlopenNetworkTests) ... ok test_fileno (__main__.urlopenNetworkTests) ... """
and there it dies with an assertion error in the bowels of Microsoft's fdopen.c. That's called by Python's posix_fdopen, here:
fp = fdopen(fd, mode);
At this point, fd is 436. MS's fdopen is unhappy because only 32 handles actually exist at this point, and 436 is bigger than that. In the release build, the MS assert doesn't (of course) trigger; instead, that 436 >= 32 causes MS's fdopen to return NULL.
The test assumes that the fileno() from a socket object can be passed to os.fdopen(). That works on Unix. But on Windows it cannot, the small ints used to refer to open files are chosen from a different (though potentially overlapping) space than the small ints used to refer to open sockets, and the two cannot be mixed. So the test should be disabled on Windows. I don't know if we can protect os.fdopen() from crashing when passed an out of range number. --Guido van Rossum (home page: http://www.python.org/~guido/)