This checks if the file descriptor is still valid. If :func:`os.fstat`
        does not raise an exception then we assume it is alive.

def isalive (self):
        '''This checks if the file descriptor is still valid. If :func:`os.fstat`
        does not raise an exception then we assume it is alive. '''

        if self.child_fd == -1:
            return False
        try:
            os.fstat(self.child_fd)
            return True
        except:
            return False