p.py

# git log --stat --name-only --pretty='hash:%H' | python p.py

import sys
from collections import defaultdict
import json

cur_hash = None
mapping = defaultdict(list)

for line in sys.stdin:

    line = line.strip()

    if not line:
        continue

    if line.startswith("hash:"):
        cur_hash = line.split(":")[-1]
        continue

    mapping[line].append(cur_hash)

json.dump(mapping, sys.stdout, indent=4)