#!/usr/bin/python3
import difflib
def get_lines(filename):
    with open(filename, 'r', encoding='utf8') as fd:
        return fd.readlines()
old_new = list(difflib.unified_diff(
    get_lines('external.old'),
    get_lines('external.new'),
))
new_old = list(difflib.unified_diff(
    get_lines('external.new'),
    get_lines('external.old'),
))
print('diff -u external.old external.new.json | wc -l')
print(len(old_new))
print('diff -u external.new external.old.json | wc -l')
print(len(new_old))

$ ./difftest.py
diff -u external.old.json external.new.json | wc -l
30854
diff -u external.new.json external.old.json | wc -l
26

$ diff -u external.old.json external.new.json | wc -l
26

$ diff -u external.new.json external.old.json | wc -l
26