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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 ubridge(self):
 """ Returns the uBridge hypervisor. :returns: instance of uBridge """


        if self._ubridge_hypervisor and not self._ubridge_hypervisor.is_running():
            self._ubridge_hypervisor = None
        return self._ubridge_hypervisor