Josh Williams You may be familiar with connecting to a database using Python, but did you know it's possible for your database itself to use Python? PostgreSQL has the ability to write functions and procedures in PL/Python, which can use Python to both work with data inside your database, and bring in information from the outside world. This tutorial-format demonstration is designed to show you how to get up and running on PL/Python, and some of the cool things you can accomplish using it.

1. (Bottom Half of Screen)
Intro to PL/Python
Josh Williams

2. What is PL/Python?
 Procedural Language INSIDE PostgreSQL
 Not a replacement for SQL
 Run manually (functions / DO in 9.0)
 or automatically (triggers)

3. Why PostgreSQL?
 Powerful, yet very fast.
 Feature rich, but you can't beat the price.
 It's future is clear!

4. Why Python?
 Easy to read. Easy to learn. Easy to use.
 Powerful, yet very fast.
 Possibly already using it outside the database.
 It's Python!!

5. Okay, enough crowd pandering
 Step 1: Configure PostgreSQL for Python
 Step 2: Install PL/Python into database(s)
 Step 3: Profit

6. 1. Configure PG for Python
 If using source, `./configure ­­with­python`
 If using packages, install ”­plpython” or ”­py...”
 In either case you need Python installed (duh)

7. Is it there?
 SELECT * FROM pg_pltemplate;
 tmplname == plpythonu
 or plpython2u
 or plpython3u

8. Wait, u?
 PL/Python is an untrusted language...
 Only DB superusers can create functions :(
 Functions can communicate outside the DB :)

9. 2. Enable Databases
 Command line: createlang plpythonu dbname
 Inside DB: CREATE LANGUAGE plpythonu;
 Hint: Install in template1
 SELECT * FROM pg_language;

10. CREATE FUNCTION...
CREATE FUNCTION function_name (....)
AS $dollarquote$ ...python here...
... $dollarquote$ LANGUAGE plpythonu;
 See ”Intro to PL/pgSQL” for construct details

11. The ...python here... bit
 Where the interesting Python­y stuff happens
 Simple processing of function parameters
 But also... Import modules (stats, XML, ASCII plot?)
 Interact with the outside world, the inside world

12. The web IN your database redux
 Need a type to represent composite RSS data
 Need RSS reader module … feedparser!
 CREATE FUNCTION … RETURNS SETOF …

13. It works!
 But 11 lines? This is Python, we can do better!
 There … Two lines (plus the module import)

14. Something a little more fancy
 Create two really basic functions:
CREATE FUNCTION pydir(text) RETURNS SETOF text...
CREATE FUNCTION isdir(text) RETURNS boolean...
 Call SRF using just SELECT pydir('/')

15. Enter Recursive Queries (8.4+)
 CTE construct: WITH RECURSIVE …
 Initial value(s) UNION recursive query
 Then SELECT … FROM cte

16. But that's usual Python stuff
 PL/Python implicitly includes module ”plpy”
 Execute SQL statements
 Generates messages/raises errors back to PG

17. Last contrived example
 Basic personal finance application
 Add a trigger: Net balance must be positive

18. Two Step Process
 CREATE FUNCTION … RETURNS trigger
 CREATE TRIGGER accounts_check AFTER
 INSERT OR UPDATE ON accounts FOR EACH
 STATEMENT EXECUTE PROCEDURE accheck();

19. Boooring
 Wait, we're using Python. We can do more!
 How about an early warning email?
 See package smtplib

20. That's PL/Python
Any questions?

21. Intro to PL/Python
http://joshwilliams.name/plpython/ (Now!)
In the mean time: joshwilliams@ij.net