xfrm.py

import sys
from collections import defaultdict

hosts_by_pkg = defaultdict(set)

for line in sys.stdin:
    line = line.strip()
    if not line:
        continue
    host, pkg = line.split()
    hosts_by_pkg[pkg].add(host)

for pkg, hosts in hosts_by_pkg.items():
    init = f'{pkg}: '
    print(init + ', '.join(hosts))
    print()