pyodbc - [unixODBC][Driver Manager]Data source name not found, and no default driver specified - pyodbc

Question

I am setting up a system to connect to an AWS Redshift database from python. I am thinking that there's something wrong in the python script because I can connect via isql. I've installed all the relevant packages, and I am able to connect via isql as follows:
$ isql rndredshift readonly ***** -v
+---------------------------------------+
| Connected! |
| |
| sql-statement |
| help [tablename] |
| quit |
| |
+---------------------------------------+
SQL> quit
However, my python script is failing to connect. Here's the script:
import pyodbc
import sys
def main():
redshift_conn_str = assemble_connection_string(
Driver='{PostgreSQL}',
Server='10.191.4.97',
ServerName='rndredshift',
Port='5439',
Database='prod',
Uid='readonly',
Pwd='*******'
)
print("===========")
print(redshift_conn_str)
print("===========")
new_conn2 = pyodbc.connect(redshift_conn_str)
print(psql.read_sql('select top 10 * from rawdb.raw_imprequest_20150101', new_conn2))
def assemble_connection_string(**kwargs):
return ';'.join([k + '=' + v for (k, v) in kwargs.items()])
if __name__ == '__main__':
sys.exit(main())
Here's the output:
===========
Uid=readonly;Database=prod;ServerName=rndredshift;Driver={PostgreSQL}; Server=10.191.4.97;Pwd=********;Port=5439
===========
Traceback (most recent call last):
File "test_redshift.py", line 24, in <module>
sys.exit(main())
File "test_redshift.py", line 17, in main
new_conn2 = pyodbc.connect(redshift_conn_str)
pyodbc.Error: ('IM002', '[IM002] [unixODBC][Driver Manager]Data source name not found, and no default driver specified (0) (SQLDriverConnectW)')
The PosgreSQL driver is installed:
$ odbcinst -q -d
[PostgreSQL]
[MySQL]
And the data source is configured:
$ odbcinst -q -s
[rndredshift]

Answer 1

If you're using DSNs, you're going to need to specify that in your connection string. Also, if you want to use DSN-less connections, I believe the keyword is SERVER and not SERVERNAME.
Try this connection string?
Uid=readonly;Database=prod;DSN=rndredshift;Driver={PostgreSQL};Pwd=********;
Make sure you specify the full server name and port in odbc.ini as well. Also, since you're using PostgreSQL, any reason you're not using the native PostgreSQL driver?
https://wiki.postgresql.org/wiki/Psycopg
Good luck!

Answer 2

Also, I've been perplexed over the ways to obtain and install the PostgreSQL driver. When I installed unixODBC, the odbcinst.ini file was created and contained an entry for the PostgreSQL driver that looked this this:
[PostgreSQL]
Description = ODBC for PostgreSQL
Driver = /usr/lib/psqlodbc.so
Setup = /usr/lib/libodbcpsqlS.so
Driver64 = /usr/lib64/psqlodbc.so
Setup64 = /usr/lib64/libodbcpsqlS.so
FileUsage = 1
However, the files for Driver and Driver64 where not on the system. So then, I installed postgresql-odbc, which gave me the missing libraries. Is there a better way to do this? As I mentioned earlier, isql works fine, so I'm still thinking it's a python issue.

Answer 3

I decided to try using the psycopg2 package, and I got a connection to work! Here's my script:
import sys
import psycopg2
def main():
conn_string = "host='10.191.4.97' dbname='prod' user='readonly' password='****' port='5439'"
print("===========")
print(conn_string)
print("===========")
new_conn2 = psycopg2.connect(conn_string)
print("Connected using psycopg2!")
if __name__ == '__main__':
sys.exit(main())
So, while I'm happy that I can connect, the question still remains about pyodbc and the PostgreSQL connection string. Thoughts?

Answer 4

Here's the connection string:
Uid=readonly;Database=prod;ServerName=rndredshift;Driver={PostgreSQL}; Server=10.191.4.97;Pwd=********;Port=5439
Using DSN instead of ServerName didn't work.