Fair warning: really splitting hairs here...

I agree that the naming could be better. Maybe ```is_valid_cidr``` might be a better name? In that case, you might want to validate that there's only one '/' in ```string_network```, that ```string_network.split('/')[1]``` is an integer between 0 and 32, and keep the implicit check that ```socket.inet_aton(string_network.split('/')[0])``` raises when it's not a valid IPv4 address. Although, I do think that ```inet_aton``` takes valid input that wouldn't make for a valid CIDR. For example, I think it'll return a valid value for the input ```"127"```.