Getting error messages from psycopg2 exceptions

Question

This is my first project using psycopg2 extensively. I'm trying to find a way to extract the psql error message for whenever a connection attempt fails. I've tested the code below will work if all the variables are set correctly, however whenever an error condition occurs (e.g. user chooses a database that doesn't exist), Python will give me the following:

I am unable to connect to the database None Traceback (most recent call last):   File "./duplicate_finder.py", line 163, in <module>     main(sys.argv[1:])   File "./duplicate_finder.py", line 142, in main     print e.diag.message_detail AttributeError: 'OperationalError' object has no attribute 'diag' 

Is there a simple, catch-all method to catch whatever error message psql generates when a connection fails, or do I need to write except blocks for multiple psycopg2 exceptions?

Extract from my script:

import sys, getopt, os, time, csv, psycopg2      ...     ...      conn_string = "host=" + dbhost + " dbname=" + database + " user=" + dbuser + " password=" + dbpass     try:         conn = psycopg2.connect(conn_string)     except psycopg2.Error as e:         print "Unable to connect!"         print e.pgerror         print e.diag.message_detail         sys.exit(1)     else:         print "Connected!"         cur = conn.cursor()         cur.execute("SELECT id, lastname, firstname, location FROM test ORDER BY ctl_upd_dttm DESC;")         print cur.fetchone()         ...         conn.close() 

Answer 1

When I try to catch exceptions, e.pgerror is always None for connection errors. The following code block gets around this by directly printing 'e'.

try:     conn = psycopg2.connect(conn_string) except psycopg2.OperationalError as e:     print('Unable to connect!\n{0}').format(e)     sys.exit(1) else:    print('Connected!')    # do stuff 

For example, in the case of password authentication failure:

Unable to connect! FATAL:  password authentication failed for user "user" 

I realize this question is a year old but hopefully might help someone in the future

Answer 2

Ended up here because of

class 'psycopg2.errors.InvalidCursorName'

on Django. If that's your case, be sure to makemigrations