<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def can_rewind(self):
 """ check if pg_rewind executable is there and that pg_controldata indicates we have either wal_log_hints or checksums turned on """

        # low-hanging fruit: check if pg_rewind configuration is there
        if not self.config.get('use_pg_rewind'):
            return False

        cmd = [self._pgcommand('pg_rewind'), '--help']
        try:
            ret = subprocess.call(cmd, stdout=open(os.devnull, 'w'), stderr=subprocess.STDOUT)
            if ret != 0:  # pg_rewind is not there, close up the shop and go home
                return False
        except OSError:
            return False
        return self.configuration_allows_rewind(self.controldata())