cidr_notation.py

#!/bin/python3

# Take an ip string and return a string representing it's binary value
#   inputs: ip_string = '192.168.1.12'
#   outputs: returns '1100000010...'
def prepBinary(ip_string):
    binary_string = ""
    ip_nums_string = ip_string.split(".");

    for ip_num in ip_nums_string:
        # creates a binary number with 8 digits .. i.e. 6 becomes 00000110, 192 becomes 11000000
        binary_string += ('{0:08b}'.format(int(ip_num)))
    return binary_string

# Calculate whether a given ip needle is in an ip haystack range
#   inputs: needle = ip string i.e. '192.168.1.21"
#           haystack= ip string with mask i.e. '192.168.1.1/24'
#   outputs: boolean
def inRange(needle, haystack):
    # prep haystack:
    #  - split off the network mask
    haystack_parts = haystack.split("/")
    haystack_mask = int(haystack_parts[1])

    # - convert the ip addresses to binary representations
    #    i.e. haystack_binary = 11000000101010000000000000000000
    #         needle_binary   = 11000000101010000000010000011011
    haystack_binary = prepBinary(haystack_parts[0])
    needle_binary = prepBinary(needle)

    # count along {mask} number of items from left to right and check they match ....
    if needle_binary[0:haystack_mask] == haystack_binary[0:haystack_mask]:
        return "true"
    return "false"

if __name__ == "__main__":
    # If I was going to get carried away, I'd check ip string inputs before passing them
    print(inRange("192.168.4.27", "192.168.0.0/16"))
    print(inRange("192.168.4.27", "192.168.1.0/24"))