Working with all connected to Panorama firewalls

[BatD2]

I would like to run certain ops command to all or to a subset of the firewalls connected to Panorama.

I first get all connected firewalls:

firewalls = panorama1.refresh_devices(only_connected=True, expand_vsys=False, include_device_groups=False)

And then I add them as Panorama children:

for fw in firewalls:
    panorama1.add(fw)

Let's say that for example I want to run' show system info' against all of them and looping over each object works:

for fw in firewalls:
    ET.dump(fw.op('show system info'))

However what will be the best way to wok with a single firewall or list of firewalls, matching serial numbers list? Is this the best aproach or am I doing something wrong?