Line messenger chat: Count number of message per month

line-chats-count-per-month.py

import re

textfile = open("./line-chat.txt", 'r')
reg_date = re.compile("\w{3}\.,\s\d{1,2}\/(\d{1,2}\/\d{4})")
reg_hour = re.compile("\d{2}:\d{2}\t")
mapSenders = {}

for line in textfile:

    matches_date = reg_date.findall(line)
    matches_hour = reg_hour.findall(line)    

    if matches_date:
        print(matches_date)
        year = matches_date[0]
        if year not in mapSenders:
            print ("changing month " + year)
            mapSenders[year] = 0

    if matches_hour:
        mapSenders[year] = mapSenders[year] + 1

for m in mapSenders:
    print (str(m) + ": " + str(mapSenders[m]))