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Re: Passing tabular data around using python functions

From: Jan Urbański <wulczer(at)wulczer(dot)org>
To: Achim Domma <domma(at)procoders(dot)net>
Cc: PG Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Passing tabular data around using python functions
Date: 2012-07-31 09:40:18
Message-ID: 5017A802.7080008@wulczer.org (view raw or flat)
Thread:
Lists: pgsql-hackers
On 30/07/12 14:33, Achim Domma wrote:
> Hi,

Hi Achim,

this list is meant for discussing the development of PostgreSQL, in the 
future you might want to ask your question on pgsql-general.

However, to answer your question:

> I call the function like this:
>
> select * from vectormatch(array(select (docid,conceptid,rank)::fps from fps where docid = 4205591))
>
> and get the following output:
>
> NOTICE:<type 'list'>
> CONTEXT:  PL/Python function "vectormatch"
> NOTICE:  ['(4205591,1,1)', '(4205591,1219,1)', ...]
> CONTEXT:  PL/Python function "vectormatch"
>
> I'm quite surprised that there are strings in the list and not tuples!? I tried my best, but I have no idea what I might be doing wrong. The main purpose of my sample/experiment is, to pass the results of a query to a function and to process it there. Any hint would be very appreciated.

Yes, it's a missing feature of PL/Python, but in your case you could 
work around it by writing your function like this:

create or replace function vectormatch(docid integer[], conceptid 
integer[], rank float4[])
     returns table(docid integer, weigth float4)
as $$
     data = zip(docid, conceptid, rank)
     plpy.notice(data)
     ...
$$ language plpythonu;

and then calling it like this:

select vectormatch(array_agg(docid), array_agg(conceptid), 
array_agg(rank)) from fps where docid = 4205591;

Cheers,
Jan

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