/opt/python3.2/lib/python3.2/site-packages/psutil/_pslinux.py:389: ResourceWarning: unclosed file <_io.FileIO name=7 mode='rb'>
  return [x for x in f.read().split('\x00') if x]

I get this while running tests.
The method in question is defined as such:

    @wrap_exceptions
    def get_process_cmdline(self):
        f = open("/proc/%s/cmdline" % self.pid)
        try:
            # return the args as a list
            return [x for x in f.read().split('\x00') if x]
        finally:
            f.close()

...therefore, I'm closing the file object (in the finally block).