How to convert a CIDR prefix to a dotted-quad netmask in Python?

Question

How can I convert a CIDR prefix to a dotted-quad netmask in Python?

For example, if the prefix is 12 I need to return 255.240.0.0.

Answer 1

You can do it like this:

def cidr(prefix):
    return socket.inet_ntoa(struct.pack(">I", (0xffffffff << (32 - prefix)) & 0xffffffff))