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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 _ensure_core_connections(self):
 """ If any host has fewer than the configured number of core connections open, attempt to open connections until that number is met. """

        for session in tuple(self.sessions):
            for pool in tuple(session._pools.values()):
                pool.ensure_core_connections()