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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def ready(self):
 """ Assumes postgres now talks to pg_ctl, but might not yet be listening or connections from psql. Test that psql is able to connect, as it occasionally takes 5-10 seconds for postgresql to start listening. """

        cmd = self._psql_cmd()
        for i in range(50, -1, -1):
            res = subprocess.call(
                cmd, stdin=DEV_NULL, stdout=DEV_NULL,
                stderr=DEV_NULL)
            if res == 0:
                break
            time.sleep(0.2)
        return i != 0