Re: python async with psycopg2

[Daniele Varrazzo]

On Fri, 17 Jul 2020 at 20:44, Rita  wrote:>

> curs = conn.cursor()
> curs.execute("LISTEN mychan0;")
> #curs.execute("LISTEN mychan1;") #fails!
> wait_select(conn)

Maybe you have to wait_select after each execute.

This example could be helpful.
https://www.psycopg.org/docs/advanced.html#asynchronous-notifications
Note that you don't need an async connection to receive notification:
a sync one, as long as is in autocommit and you are using an I/O
completion function to wait for readiness, works as well.

-- Daniele

python async with psycopg2

[Rita]

I am trying to listen to multiple channels thru pg_notify mechanism.

select pg_notify('mychan0',foo');
select pg_notify('mychan'1,'bar');

In python I have something like this

import select,time
import psycopg2
import psycopg2.extensions
from psycopg2.extras import wait_select

DSN="dbname=mydb user=user host=localhost"

def main():

conn = psycopg2.connect(DSN,async_=True)
wait_select(conn)
curs = conn.cursor()
curs.execute("LISTEN mychan0;")
#curs.execute("LISTEN mychan1;") #fails!
wait_select(conn)
while True:
wait_select(conn)
while conn.notifies:
print("Notify: %s"%conn.notifies.pop().payload)
time.sleep(1)
conn.close()

I keep getting

psycopg2.ProgrammingError: execute cannot be used while an asynchronous
query is underway

I prefer to stick with psycopg2 library instead of a wrapper.
What am I doing wrong?

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