python wait till something in postgres database changes

Question

I have a simple postgres database, here's an example table

id	created_at	whatever
1	2020-12-22 21:47:20.159781	something
2	2020-12-22 22:13:46.872718	anything

how can I do that whenever something changes in it, it triggers a function in my script?

Answer 1

Postgres has the notify and listen procedures you can read up on here: notify and listen . Their use in Python is best (and I believe only) through pyscopg2

pip install psycopg2

import select
import psycopg2
import psycopg2.extensions


cnct = psycopg2.connect(DSN)
cnct.set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT)

cursor = cnct.cursor()
cursor.execute("LISTEN channel;")
print("Pending notification from 'channel'...")


while True:
    if select.select([cnct],[],[],5) == ([],[],[]):
        print("Channel timed out.")
    else:
        cnct.poll()
        while cnct.notifies:
            notif = cnct.notifies.pop(0)
            print("Received NOTIFY:", notif.pid, notif.channel, notif.payload)

Forgot to mention:: This information was from what I versed myself with on the Psycopg2 Documentation and you might need to more elaborately familiarize yourself with using Pyscopg2 there.