def _debug(self, out, print_prefix=True):
        """ Print out to stderr, if debugging is enabled. """
        if self.debug:
            if print_prefix:
                pre = self.__class__.__name__
                if hasattr(self, 'debug_prefix'):
                    pre = getattr(self, 'debug_prefix')
                sys.stderr.write("%s: " % pre)
            sys.stderr.write(out)
Print out to stderr, if debugging is enabled.