plpython return setof and yield

On Sunday 16 August 2009 5:13:51 pm Nuno Mota wrote:

Hi,

I am kind of new into python, and I have been trying to port some plperl
functions into plpython, but I've run up into a problem.

Imagine the following plpython code.

CREATE OR REPLACE FUNCTION greet (how text)
RETURNS SETOF greeting
AS $$
rv = plpy.execute("SELECT 1")

for article in range(10) :
for other in range(10) :
if (other == 1) : continue
yield([article,other])
$$LANGUAGE plpythonu;

When executing the function on the psql console I always the this error.

netbo-dev=# select * from greet('Nuno');
ERROR: error fetching next item from iterator

If I comment the first line:

rv = plpy.execute("select 1")

Turning the code into this:

CREATE OR REPLACE FUNCTION greet (how text)
RETURNS SETOF greeting
AS $$
#rv = plpy.execute("SELECT 1")

for article in range(10) :
for other in range(10) :
if (other == 1) : continue
yield([article,other])
$$LANGUAGE plpythonu;

The code works:

netbo-dev=# select * from greet('Nuno');
how | who
-----+-----
0 | 0
0 | 2
0 | 3
0 | 4
0 | 5
0 | 6

I know the example code is not the best, but What I was tryng to do is
execute some SQL then process it and return it back.

I also know I could just generate the rows and place them in a list and
then return it, but I would like to know why the yield function does'nt
work in this case.

This was tried on with:

PostgreSQL 8.3.7 and Python 2.5.1

Thanks,
Nuno Mota

As a guess, in the first example you have the function creating two result sets
without declaring which one to return. In the second example you are using the
generator alone.

--
Adrian Klaver
aklaver@comcast.net

Thank you very much,

Can i ask one more question ?

How do I declare the correct result set to return, this in first example
code, is it possible ?

Thank you again,
Nuno Mota

On Mon, Aug 17, 2009 at 3:21 PM, Adrian Klaver <aklaver@comcast.net> wrote:

On Sunday 16 August 2009 5:13:51 pm Nuno Mota wrote:

Hi,

I am kind of new into python, and I have been trying to port some plperl
functions into plpython, but I've run up into a problem.

Imagine the following plpython code.

CREATE OR REPLACE FUNCTION greet (how text)
RETURNS SETOF greeting
AS $$
rv = plpy.execute("SELECT 1")

for article in range(10) :
for other in range(10) :
if (other == 1) : continue
yield([article,other])
$$LANGUAGE plpythonu;

When executing the function on the psql console I always the this error.

netbo-dev=# select * from greet('Nuno');
ERROR: error fetching next item from iterator

If I comment the first line:

rv = plpy.execute("select 1")

Turning the code into this:

CREATE OR REPLACE FUNCTION greet (how text)
RETURNS SETOF greeting
AS $$
#rv = plpy.execute("SELECT 1")

for article in range(10) :
for other in range(10) :
if (other == 1) : continue
yield([article,other])
$$LANGUAGE plpythonu;

The code works:

netbo-dev=# select * from greet('Nuno');
how | who
-----+-----
0 | 0
0 | 2
0 | 3
0 | 4
0 | 5
0 | 6

I know the example code is not the best, but What I was tryng to do is
execute some SQL then process it and return it back.

I also know I could just generate the rows and place them in a list and
then return it, but I would like to know why the yield function does'nt
work in this case.

This was tried on with:

PostgreSQL 8.3.7 and Python 2.5.1

Thanks,
Nuno Mota

As a guess, in the first example you have the function creating two result
sets
without declaring which one to return. In the second example you are using
the
generator alone.

--
Adrian Klaver
aklaver@comcast.net

--
Nuno Mota <nmota@net-bo.com>

Management Solutions for POS
Tlf: 351 225322000
Mob: 351 936272176
Fax: 351 226177662
http://www.net-bo.com

----- "Nuno Mota" <nmota@net-bo.com> wrote:

Thank you very much,

Can i ask one more question ?

How do I declare the correct result set to return, this in first
example code, is it possible ?

Thank you again,
Nuno Mota

From here:

http://www.postgresql.org/docs/8.3/interactive/plpython-funcs.html

"The result is returned from the Python code in the usual way, with return or yield (in case of a result-set statement). "

Adrian Klaver
aklaver@comcast.net

I have fixed the problem populating a list and returning it.

Well I guess I have to learn a litte bit more of python to understand how to
use yield when using multiple result sets.

Thank you anyway

On Mon, Aug 17, 2009 at 7:23 PM, Adrian Klaver <aklaver@comcast.net> wrote:

----- "Nuno Mota" <nmota@net-bo.com> wrote:

Thank you very much,

Can i ask one more question ?

How do I declare the correct result set to return, this in first
example code, is it possible ?

Thank you again,
Nuno Mota

From here:
http://www.postgresql.org/docs/8.3/interactive/plpython-funcs.html

"The result is returned from the Python code in the usual way, with return
or yield (in case of a result-set statement). "

Adrian Klaver
aklaver@comcast.net

--
Nuno Mota <nmota@net-bo.com>

Management Solutions for POS
Tlf: 351 225322000
Mob: 351 936272176
Fax: 351 226177662
http://www.net-bo.com

Ok, now I think I understand since I already have a result set from the
query I cannot use yield.

The other example works because I am generating only one result set.

On Mon, Aug 17, 2009 at 7:55 PM, Nuno Mota <nmota@net-bo.com> wrote:

I have fixed the problem populating a list and returning it.

Well I guess I have to learn a litte bit more of python to understand how
to use yield when using multiple result sets.

Thank you anyway

On Mon, Aug 17, 2009 at 7:23 PM, Adrian Klaver <aklaver@comcast.net>wrote:

----- "Nuno Mota" <nmota@net-bo.com> wrote:

Thank you very much,

Can i ask one more question ?

How do I declare the correct result set to return, this in first
example code, is it possible ?

Thank you again,
Nuno Mota

From here:
http://www.postgresql.org/docs/8.3/interactive/plpython-funcs.html

"The result is returned from the Python code in the usual way, with return
or yield (in case of a result-set statement). "

Adrian Klaver
aklaver@comcast.net

--
Nuno Mota <nmota@net-bo.com>

Management Solutions for POS
Tlf: 351 225322000
Mob: 351 936272176
Fax: 351 226177662
http://www.net-bo.com

--
Nuno Mota <nmota@net-bo.com>

Management Solutions for POS
Tlf: 351 225322000
Mob: 351 936272176
Fax: 351 226177662
http://www.net-bo.com