[forwarded from http://bugs.debian.org/283108]

Write errors on stdout may be ignored, and hence may 
result in loss of valuable user data. 
 
Here's a quick demo: 
 
$ ./close-bug 
foo 
$ ./close-bug > /dev/full && echo unreported write failure 
unreported write failure 
$ cat close-bug 
#!/usr/bin/python 
import sys 
def main (): 
    try: 
        print 'foo' 
        sys.stdout.close () 
    except IOError, e: 
        sys.stderr.write ('write failed: %s\n' % e) 
        sys.exit (1) 
 
if __name__ == '__main__': 
    main () 


This particular failure comes from the following
unchecked fflush 
of stdout in pythonrun.c: 
 
  static void 
  call_ll_exitfuncs(void) 
  { 
          while (nexitfuncs > 0) 
                  (*exitfuncs[--nexitfuncs])(); 
 
          fflush(stdout); 
          fflush(stderr); 
  } 
 
Flushing the stream manually, python does raise an
exception.

Please note that simply adding a test for fflush
failure is 
not sufficient.  If you change the above to do this: 
 
  if (fflush(stdout) != 0) 
    { 
      ...handle error... 
    } 
 
It will appear to solve the problem. 
But here is a counterexample: 
 
import sys 
def main (): 
    try: 
        print "x" * 4095 
        print 
        sys.stdout.close () 
    except IOError, e: 
        sys.stderr.write ('write failed: %s\n' % e) 
        sys.exit (1) 

if __name__ == '__main__': 
    main () 
 
If you run the above with stdout redirected to /dev/full, 
it will silently succeed (exit 0) in spite of a write
failure. 
That's what happens on my debian unstable system. 
 
Instead of just checking the fflush return value, 
it should also check ferror: 
 
  if (fflush(stdout) != 0 || ferror(stdout)) 
    { 
      ...handle error... 
    }