How to catch specific Postgres exceptions in Python psycopg2

Question

Default psycopg2 error messages are too broad. Most of the time it simply throws:

psycopg2.OperationalError

without any additional information. So it is hard to guess, what was the real reason of the error - either incorrect user credentials, or simply the fact the server is not running. So, I need some more appropriate error handling, like error codes in pymysql library.

I've seen this page, but it does not help. When I do

except Exception as err:
    print(err.pgcode)

it always prints None. And as for errorcodes it is simply undefined. I tried to import it, but failed. So, I need some help.

Answer 1

For anyone looking a quick answer:

Short Answer

import traceback  # Just to show the full traceback
from psycopg2 import errors

InFailedSqlTransaction = errors.lookup('25P02')

            try:
                feed = self._create_feed(data)
            except InFailedSqlTransaction:
                traceback.print_exc()
                self._cr.rollback()
                pass # Continue / throw ...

Long Answer

1. Go to psycopg2 -> erros.py you will find the lookup function lookup(code).
2. Go to psycopg2\_psycopg\__init__.py in sqlstate_errors you will find all codes to add as string into the lookup function.