The current semantic of io streams is to swallow IOErrors on close(), eg. in _pyio from the trunk, we have each time constructs like:
try:
     self.flush()
except IOError:
     pass  # If flush() fails, just give up

and in C files :
        /* If flush() fails, just give up */
        if (PyErr_ExceptionMatches(PyExc_IOError))
            PyErr_Clear();

I'd rather advocate letting exceptions flow, as users have the right to know if their io operations lost bytes.
Below is a test case for these swallowed exceptions.


PS : issues like http://bugs.python.org/issue7640 are actually much more crucial, so we shall let them higher priority