This script will process the json dump from Google Takeout to extract all messages sent between two people. Before extracting the conversation you need to know the conversation_id.

hangout-filter.py

# example:
# python hangout-filter.py Hangouts.json Ugw3axd-nDFKCvFsDi94AaABAQ | sort | tr '\n' ' ' > words.txt

# !/usr/bin/env python

import json
import argparse
import dateutil.parser
import re
import time

parser = argparse.ArgumentParser(
	description='Print conversations in readable format.')
parser.add_argument('filename')
parser.add_argument('conversation_id')
args = parser.parse_args()

data = json.load(open(args.filename))

states = data['conversations']
for state in states:
	conversation_state = state['conversation']
	if 'events' in state:
		conversations = state['events']
		for conversation in conversations:
			if 'chat_message' in conversation:
					message_content = conversation['chat_message']['message_content']
					if 'segment' in message_content:
						segment = message_content['segment']
						for line in segment:
							conversation_id = conversation['conversation_id']['id']
							if conversation_id == args.conversation_id:
								timestamp = time.localtime(int(conversation['timestamp']) / 1000000)
								user_id = conversation['sender_id']['gaia_id']
								try:
									uname = [p['fallback_name'] for p in conversation_state['conversation']['participant_data'] if p['id']['gaia_id'] == user_id][0]
								except:
									uname = user_id
								if 'text' in line:
									msg = line['text']
								elif 'type' in line and line['type'] == 'LINE_BREAK':
									msg = ''
								else:
									msg = line
								out = '{:<12}'.format(uname) + ' @ ' + time.asctime(timestamp) + ': ' + msg
								print(out.encode('ascii', 'ignore'))