Python is often described as a "batteries included" kind of language, and this is no exception.

There's a module just for IP address manipulation and another module to generate random numbers. Put together, they do exactly what you want, in a way that's slightly more readable (IMO).

For this example, I'll assume that the variable v contains either 4 or 6.

from random import getrandbits

from ipaddress import IPv4Address, IPv6Address



if v == 4:

    bits = getrandbits(32) # generates an integer with 32 random bits

    addr = IPv4Address(bits) # instances an IPv4Address object from those bits

    addr_str = str(addr) # get the IPv4Address object's string representation

elif v == 6:

    bits = getrandbits(128) # generates an integer with 128 random bits

    addr = IPv6Address(bits) # instances an IPv6Address object from those bits

    # .compressed contains the short version of the IPv6 address

    # str(addr) always returns the short address

    # .exploded is the opposite of this, always returning the full address with all-zero groups and so on

    addr_str = addr.compressed 



print(addr_str)

Here, addr_str will hold a fully random IPv4 or IPv6 address.

You can even generate random addresses from a subnet like this:

from random import getrandbits

from ipaddress import IPv4Network, IPv4Address



# network containing all addresses from 10.0.0.0 to 10.0.0.255

subnet = IPv4Network("10.0.0.0/24") 



# subnet.max_prefixlen contains 32 for IPv4 subnets and 128 for IPv6 subnets

# subnet.prefixlen is 24 in this case, so we'll generate only 8 random bits

bits = getrandbits(subnet.max_prefixlen - subnet.prefixlen)



# here, we combine the subnet and the random bits

# to get an IP address from the previously specified subnet

addr = IPv4Address(subnet.network_address + bits)

addr_str = str(addr)



print(addr_str)

Here, addr_str will always contain IP addresses like 10.0.0.184, 10.0.0.42 and so on. It works the same way with IPv6 addresses, except in that case you'd have to import IPv6Network and IPv6Address instead.

Here are a few ideas about your code.

Check for command line arguments

The code fails with an exception if it's invoked with no command line arguments because it attempts to use argv[1] and there isn't any. I'd suggest that it would be nice to print a "usage" message if the user enters either an invalid or no argument.

Use a list comprehension

List comprehensions are extremely useful and very Pythonic. It's really good to become proficient with them. Here's how to use one to generate a random IPv4 address:

'.'.join([str(randint(0,255)) for x in range(4)])

And an IPv6 address is a little trickier because we need hex digits.

':'.join([hex(randint(2**16,2**17))[-4:] for x in range(8)])

That works because randint generates a number in the range 0x10000 to 0x20000 and we then pick off the last four hex digits.

For someone not familiar with Python, you have picked pretty good habits. Not everyone uses functions or the if __name__ == '__main__' guard first try.

That being said, I think it would make more sense to provide 2 functions instead of a single one: random_ipv4 and random_ipv6.

You could also feed generator expressions to join. They are both faster to process than + for + append and easier to read:

def random_ipv4():

    return '.'.join(str(randint(0,255)) for _ in range(4))





def random_ipv6():

    return ':'.join(

            ''.join(choice(hexdigits).lower() for _ in range(4))

            for _ in range(8)

    )

The only thing left being to properly validate that the input is either 4 or 6:

if __name__ == '__main__':

    if len(sys.argv) < 2:

        sys.exit('Usage: python random_ip.py VERSION')



    version = sys.argv[1]

    if version == '4':

        print(random_ipv4())

    elif version == '6':

        print(random_ipv6())

    else:

        sys.exit('VERSION should be 4 or 6, not {}'.format(version))

Check for invalid outputs, and regenerate them.

It's possible that you'll produce an output that's reserved for a particular purpose, such as loopback (127.0.0.1 or ::1) or broadcast (255.255.255.255, ff02::1, ff02::2). Build in knowledge of such addresses, and if you find you've produced one, then replace it. You can do that recursively:

def make_address(v):

    address = random_ip(v)

    if is_reserved(address):

        return make_address(v)

    return address

Validate the input: At present, your program

• aborts with IndexError if called without arguments,


• aborts with ValueError if called with a non-integer argument,


• prints None if called with an integer argument that is not 4
  or 6.

Missing or invalid arguments should print a helpful error message.
Most Unix command-line tools print the message to the standard error
and terminate with a non-zero exit status in the case of a failure.

It would be easier to compare the given argument against the
strings "4" and "6" instead of converting it to an integer
(which can fail).

Use list comprehension instead of appending to an array in a loop.
Use _ as iterator variable if the concrete value is not needed.

As an example, the "IPv4" case can be implemented as

if v == 4:

    return '.'.join(str(randint(0,255)) for _ in range(4))

Since you already got a couple of answers telling you to validate your inputs, here is a way how to do it using the argparse module:

import argparse



if __name__ == "__main__":

    parser = argparse.ArgumentParser()

    parser.add_argument('-v',

                        type=int,

                        choices=(4, 6),

                        default=4,

                        help="Whether to generate a random IPv4 or IPv6 address. Default: IPv4.")

    args = parser.parse_args()

    print(random_ip(args.v))

You can then use it on the command line like this:

./randip

./randip -v 4

./randip -v4

./randip -v 6

If you do anything else, a helpful usage message is printed:

usage: [-h] [-v {4,6}]



optional arguments:

  -h, --help  show this help message and exit

  -v {4,6}    Whether to generate a random IPv4 or IPv6 address. Default:

              IPv4.