The premise of the issue is this: if IDLE is started with 'pythonx', then running 'filex' from a IDLE editor is equivalent to running "python x -i filex" at a command line.  For instance, loading test.__main__ into an editor and running should give the same result as 
f:/python/dev> 36\pcbuild\win32\python_d.exe -i 36\Lib\test.__main__

However, 
Traceback (most recent call last):
  File "F:\Python\dev\36\Lib\test\__main__.py", line 2, in <module>
    main()
  File "F:\Python\dev\36\lib\test\libregrtest\main.py", line 508, in main
    Regrtest().main(tests=tests, **kwargs)
  File "F:\Python\dev\36\lib\test\libregrtest\main.py", line 446, in main
    self._main(tests, kwargs)
  File "F:\Python\dev\36\lib\test\libregrtest\main.py", line 458, in _main
    setup_tests(self.ns)
  File "F:\Python\dev\36\lib\test\libregrtest\setup.py", line 18, in setup_tests
    faulthandler.enable(all_threads=True)
io.UnsupportedOperation: fileno

The pseudofile socket wrappers are not real files with a fileno.  I should take a better look as sys.stdout and _stdout (and stderr) when connected to a console,