python script to organize big list of subdomains

dorg.py

#!/usr/bin/env python3
import re, sys, json


# usage: dorg.py subdomains_list.txt domain_name
# python3 dorg.py example_com_subs.txt example.com

file_path = sys.argv[1]
domain = sys.argv[2]
pattern = '[a-zA-Z0-9\-]+\.' + domain.replace('.', '\.')


def extract(file_path, pattern):
    domains = []
    fdomains = set()
    with open(file_path) as dlist:
        for dom in dlist:
            domains.append(dom.split('\n')[0])
    for dom in domains:
        rx = re.findall(pattern, dom)
        try:
            fdomains.add(rx[0])
        except IndexError:
            pass
    return domains, sorted(fdomains)


def organize(data):
    domains = data[0]
    fdomains = data[1]
    out = {}
    for d in fdomains:
        out[d] = []

    for dom in domains:
        if re.search(pattern, dom):
            out[re.findall(pattern, dom)[0]].append(dom)
    return json.dumps(out)


print(organize(extract(file_path, pattern)))