write-eol.py

#!/usr/bin/env python3

import sys, os

def fix_eol(filename):
    with open(filename) as f:
        contents = f.read()

    if not contents.endswith("\n"):
        contents += "\n"

    with open(filename, "w") as f:
        f.write(contents)

if len(sys.argv) > 1:
    fix_eol(sys.argv[1])

else:
    for filename in os.listdir():
        if filename.endswith(".json"):
            fix_eol(filename)