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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 set_qemu_symbol(self):
 """ Set the appropriate symbol for QEMU Devices """

        valid_devices = {'ASA': 'asa', 'PIX': 'PIX_firewall',
                         'JUNOS': 'router', 'IDS': 'ids'}
        if self.device_info['from'] in valid_devices \
                and 'default_symbol' not in self.node \
                and 'hover_symbol' not in self.node:
            self.set_symbol(valid_devices[self.device_info['from']])