Python countryblock with threshold

countryblock.py

import requests, argparse, pathlib
from itertools import accumulate
from operator import itemgetter


def build_subnet_list(country, threshold):
    """
    Return a list of the largest subnets from the designated
    country that provide coverage at least up to the threshold amount
    """
    url = "https://geoblocks.dalleyfamily.net/api.php"
    data = {'countries': country, 'aggregate': 'yes', 'ipver': '4', 'format': 'cidr', 'outputas': 'plaintext'}
    request = requests.get(url, params = data)
    assert request.status_code == 200

    # Split subnets by CIDR and sort by size of subnet
    subnets = [tuple([sub, int(sub.split('/')[1])]) for sub in iter(request.text.splitlines())]
    sort_subnets = sorted(subnets, key=itemgetter(1))
    # Build a list of how many ips are in each subnet
    ips = [2**(32-sub[1]) for sub in sort_subnets]
    total = sum(ips)
    print("{} subnets ({} ips) in {}".format(len(subnets), total, country))
    
    # Build list of accumulating subnet coverage and find threshold
    ip_percent = [r/total for r in accumulate(ips)]
    for n, percent in enumerate(ip_percent):
        if percent >= threshold:
            break
        
    print("{} subnets cover {:.2%} of ips".format(n, ip_percent[n]))

    filter_list = [sub[0] for sub in sort_subnets[:n]]
    return filter_list


# get args with argparse library:
# https://docs.python.org/3/library/argparse.html
parser = argparse.ArgumentParser(description='Build a list of subnets to block in CN/AU to avoid egress fees in gcloud')
parser.add_argument('env', type=pathlib.Path, help='specify an .env file to write the blocklist to - the ENV variables will be appended to the end')
parser.add_argument('-t', '--threshold', type=int, metavar='percentage', default=95, nargs='?', help='the percentage of ips you want to cover with the blocklist (default: %(default)s)')
args = parser.parse_args()


cn = build_subnet_list('CN', args.threshold/100)
au = build_subnet_list('AU', args.threshold/100)

with args.env.open('a') as f:
    f.write('CN_BLOCK="' + ' '.join(cn) + '"\n')
    f.write('AU_BLOCK="' + ' '.join(au) + '"\n')