This snippet let my interpreter crash immediately:

> import sys, io
> io.open(sys.stdout.fileno(), 'wb')
> fd.close()
> sys.stdout.write("now writing on stdout will cause a crash")

That's happened on
Python 2.7.5 (default, May 15 2013, 22:43:36) [MSC v.1500 32 bit (Intel)] on win32
Windows 7 SP1 x64

The same code let Python 3.3.2 throw an exception like this:
Exception OSError: OSError(9, 'Bad file descriptor') in <_io.TextIOWrapper name='<stdout>' mode='w' encoding='cp850'> ignored