net_mask.py

def net_mask(cidr):
    cidr, mask = cidr.split('/')
    mask = int(mask)
    bin_mask_str = mask * '1' + (32 - mask) * '0'
    mask_lst = [int(bin_mask_str[n*8:(n+1)*8], 2) for n in range(4)]
    net_addr = []
    broadcast = []
    for oct in zip(cidr.split('.'), mask_lst):
        net_addr.append(int(oct[0]) & oct[1])
        broadcast.append(int(oct[0]) | (255 - oct[1]))
    return '.'.join(map(str, net_addr)), '.'.join(map(str, broadcast))


# example
net_mask('192.168.23.16/21')