psycopg2 asynchronous cache updates w. LISTEN/NOTIFY and tcn

cats.py

# -*- coding: utf-8 -*-
"""
Created on Sun Nov 13 00:00:06 2016
@author: ergo
"""

import select
import psycopg2
import psycopg2.extensions
import threading
from time import sleep

def populate_cache(conn):
    curs = conn.cursor()    
    curs.execute('SELECT face_name, id FROM cats;')
    cats = curs.fetchall()
    curs.close()
    cats = dict(cats)

    return cats
    
    
def insert(conn, cats, v):
    curs = conn.cursor()    
    curs.execute('SELECT face_name, id FROM cats WHERE face_name = %s;', (v,))
    val = curs.fetchone()
    curs.close()
    
    cats[val[0]] = val[1]


def update(conn, cats, v):
    curs = conn.cursor()    
    curs.execute('SELECT face_name FROM cats WHERE id = %s;', (cats[v],))
    val = curs.fetchone()
    curs.close()
    
    cats[val[0]] = cats.pop(v)
    
    
def notify(conn, cats):
    while True:
        if select.select([conn],[],[],1) != ([],[],[]):
            conn.poll()
        if conn.notifies:
                #print "Must refresh cache"
                while conn.notifies:
                    notify = conn.notifies.pop(0)
                    #print "Got NOTIFY:", notify.pid, notify.channel, notify.payload
                    ret = notify.payload.split(',')
            
                    #print ret

                    op = ret[1]
                    v = ret[2].split('=')[1].replace("'",'')
                    if op == 'I':
                        insert(conn, cats, v)
                    elif op == 'D':
                        del cats[v]
                    elif op == 'U':
                        update(conn, cats, v)

                #print cats.keys()


conn = psycopg2.connect("host=<host> dbname=<database> user=<user> password=<password>")
conn.set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT)

curs = conn.cursor()
curs.execute("LISTEN cats;")
curs.close()

print "Waiting for notifications on channel 'cats'"

cats = populate_cache(conn)

t = threading.Thread(target=notify, args=(conn,cats))

t.daemon = True

t.start()

while True:
    print cats.keys()
    sleep(10)