I have tested your patch with 3.5, and it works fine, although I did have to make a minor change to get test_os to pass.  In test_os.py you had:

...
USE_GETENTROPY = ((sysconfig.get_config_var('HAVE_GETENTROPY') == 1)
                  and not sys.platform.startswith("sunos"))
HAVE_GETRANDOM = (sysconfig.get_config_var('HAVE_GETRANDOM_SYSCALL') == 1)
 
@unittest.skipIf(USE_GETENTROPY,
                 "getentropy() does not use a file descriptor")
@unittest.skipIf(HAVE_GETRANDOM,
                 "getrandom() does not use a file descriptor")
...

whereas I came up with this:

...
USE_GETENTROPY = ((sysconfig.get_config_var('HAVE_GETENTROPY') == 1)
                  and not sys.platform.startswith("sunos"))
HAVE_GETRANDOM = (sysconfig.get_config_var('HAVE_GETRANDOM') == 1)
HAVE_GETRANDOM_SYSCALL = (sysconfig.get_config_var('HAVE_GETRANDOM_SYSCALL') == 1)

@unittest.skipIf(USE_GETENTROPY,
                 "getentropy() does not use a file descriptor")
@unittest.skipIf(HAVE_GETRANDOM,
                 "getrandom() does not use a file descriptor")
@unittest.skipIf(HAVE_GETRANDOM_SYSCALL,
                 "getrandom() does not use a file descriptor")
...