How do I translate PostgreSQL OID using python

Question

I am having bit of trouble with the psycopg2 Python module. I wrote a small code to extract some information from PostgreSQL table using psycopg2 module. I want to know the data type for each columns in the table:

import os, psycopg2, getpass, sys, string

userpass = getpass.getpass()

# Connect to the database
conn = psycopg2.connect("host=hostname dbname=db user=username password=%s" %  (userpass))
cur = conn.cursor()
cur.execute("SELECT * FROM database.table;")

fieldTypes = [desc[1] for desc in cur.description]

print fieldTypes

When I execute this code, I get a list of integers (i.e. OIDs). Is there a way to convert this into something that's more understandable (e.g. 'str','int','bool' and so forth).

Answer 1

You can convert the "OID" to text by simply casting - provided the OID (Object Identifier) is actually a regtype (the OID-subtype for registered types) like you would get from the function pg_typeof().

Postgres will normally display values of the data type regtype as text to the user. Example:

SELECT pg_typeof('2013-1-1'::date);
 pg_typeof
-----------
 date

While internally it is an OID:

SELECT pg_typeof('2013-1-1'::date)::oid;
 pg_typeof
-----------
      1082

If your client does not do the same you can force it with an explicit cast:

SELECT pg_typeof('2013-1-1'::date)::text;
SELECT 1082::regtype::text;

Get types of all columns from system catalog

It's unclear how you actually retrieve the types. Consider this query to get full information:

SELECT attname
     , atttypid::regtype AS base_type
     , format_type(atttypid, atttypmod) AS full_type
FROM   pg_catalog.pg_attribute
WHERE  attrelid = 'public.tbl'::regclass  -- your table name here
AND    attnum > 0
AND    NOT attisdropped
ORDER  BY attnum;

  attname   |          base_type          |         full_type
------------+-----------------------------+-----------------------------
 age_id     | integer                     | integer
 age        | text                        | text
 ageabk     | character                   | character(2)
 foo        | boolean                     | boolean
 log_up     | timestamp without time zone | timestamp without time zone

Note that format_type(..) displays the type including modifiers.