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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 validate(self):
        '''Validate that devices are each trusted by one another

        :param kwargs: dict -- keyword args for devices and partition
        :raises: DeviceNotTrusted
        '''

        self._populate_domain()
        missing = []
        for domain_device in self.domain:
            for truster, trustees in iteritems(self.domain):
                if domain_device not in trustees:
                    missing.append((domain_device, truster, trustees))

        if missing:
            msg = ''
            for item in missing:
                msg += '\n%r is not trusted by %r, which trusts: %r' % \
                    (item[0], item[1], item[2])
            raise DeviceNotTrusted(msg)
        self.device_group = DeviceGroup(
            devices=self.devices,
            device_group_name=self.device_group_name,
            device_group_type=self.device_group_type,
            device_group_partition=self.partition
        )