Re: plpython3 - Mailing list pgsql-hackers

On Jan 14, 2010, at 7:08 PM, Greg Smith wrote:
> So more targeted examples like you're considering now would help.

Here's the first example. This covers an advantage of function modules.

This is a conversion of a plpythonu function published to the wiki:
http://wiki.postgresql.org/wiki/Google_Translate

In the above link, the code is executed in the body of a Python function.
Please see plpython's documentation if you don't understand what I mean by that.

The effect of this is that every time the FUNCTION is called from PG, the import statements are ran, a new class
object,UrlOpener, is created, and a new function object, translate, is created. Granted, a minor amount of overhead in
thiscase, but the point is that in order to avoid it the author would have to use SD: 

if "urlopener" in SD:UrlOpener = SD["urlopener"]
else:class UrlOpener(urllib.UrlOpener): ...SD["urlopener"] = UrlOpener

While some may consider this a minor inconvenience, the problem is that *setup code is common*, so it's, at least, a
ratherfrequent, minor inconvenience. 


With function modules, users have a module body to run any necessary setup code.


Now, WRT the actual example code, I'm not suggesting that either example is ideal. Only that it should *help* identify
oneparticular advantage of function modules. 

CREATE OR REPLACE FUNCTION public.gtranslate(src text, target text, phrase text)RETURNS textLANGUAGE plpython3u
AS $function$
from urllib.request import URLopener
from urllib.parse import quote_plus
import json

base_uri = "http://ajax.googleapis.com/ajax/services/language/translate?"

class UrlOpener(URLopener):   version = "py-gtranslate/1.0"
urlopen = UrlOpener().open

equal_fmt = '{0}={1}'.format

@pytypes
def main(src, to, phrase):   args = (       ('v', '1.0'),       ('langpair', quote_plus(src + '|' + to)),       ('q',
quote_plus(phrase)),  )   argstring = '&'.join([equal_fmt(k,v) for (k,v) in args]) 
   resp = urlopen(base_uri + argstring).read()   resp = json.loads(resp.decode('utf-8'))   try:       return
resp['responseData']['translatedText']  except:       # should probably warn about failed translation       return
phrase
$function$;


pl_regression=# SELECT gtranslate('en', 'es', 'i like coffee');   gtranslate
------------------Me gusta el café
(1 row)

pl_regression=# SELECT gtranslate('en', 'de', 'i like coffee');  gtranslate
----------------Ich mag Kaffee
(1 row)