getting nets

vms.py

In [1]: class vm(object):
   ...:     def __init__(self, nets):
   ...:         self.nets = nets
   ...:         

In [2]: vms = [ vm(nets=['1', '2']), vm(nets=['2', '9']), vm(nets=['3', '2']) ]

In [3]: set((net for vm in vms for net in vm.nets))
Out[3]: {'1', '2', '3', '9'}