Simple commandline filesystem chat

filechat.py

import os
import argparse
import json
from datetime import datetime
from jose import jwt
parser = argparse.ArgumentParser()
parser.add_argument('--send', '-s',dest='message',nargs=1, help="give a message to write to the file")
parser.add_argument('--listen', '-l',action="store_true", help="listens to changes to the file")
parser.add_argument('--file', '-f',dest='file',nargs=1,default="filechat",help="destination for the send and listen file, defaults to ./filechat")

class Listener(object):
    def __init__(self,filename):
        self._cached_stamp = 0
        self.filename = filename

    def update(self):
        stamp = os.stat(self.filename).st_mtime
        if stamp != self._cached_stamp:
            self._cached_stamp = stamp
            lines = open(self.filename,"r").readlines()
            #don't read if the file is empty
            if not lines:
            	return

            token = lines[-1].rstrip()
            j = jwt.decode(token, 'secret', algorithms=['HS256'])
            #simply time stamp
            d = datetime.strptime(j['time'],'%Y-%m-%dT%H:%M:%S').strftime('%H:%M')
            print(d + " : " + j['message'])
def setup():
	opts = parser.parse_args()
	#create file
	if not os.path.exists(opts.file):
		print("creating")
		f= open(opts.file, "w").close()
	if opts.message:
		if authenticate():
			send(opts.file, opts.message[0])
		else:
			print('Failed to Authenticate, are you an Admin?') 
	if opts.listen:
		listen(opts.file)

def authenticate():
	return True

def listen(filename):
	l = Listener(filename)
	while True:
		l.update()
def send(file,message):
	with open(file,"a") as f:
		token = jwt.encode({'message': message, 'time':datetime.now().strftime('%Y-%m-%dT%H:%M:%S')}, 'secret', algorithm='HS256')
		f.write(token+"\n")

if __name__ == "__main__":
	setup()