simple_ip_calc.py

def get_mask(ip1, ip2):
    mask = []
    ip1_split = ip1.split('.')
    ip1_split[-1] = str(int(ip1_split[-1]) - 1)
    ip2_split = ip2.split('.')
    ip2_split[-1] = str(int(ip2_split[-1]) + 1)
    for i, j in zip(ip1_split, ip2_split):
        mask.append(str(255 - (int(j) - int(i))))
    return '.'.join(mask)


test_list = [
['10.10.10.1', '10.10.10.254'],
['10.10.10.17', '10.10.10.30'],
['10.10.0.1', '10.10.3.254'],
['10.240.0.1', '10.243.255.254']
]

for ip1, ip2 in test_list:
    get_mask(ip1, ip2)