BUG #5232: plpythonu s=s.op() raises an exception

"David Gardner" <dgardner@creatureshop.com> writes:

CREATE OR REPLACE FUNCTION pyreplace(src text,s text)
RETURNS text AS
$BODY$
try:
src=src.replace(s,'')
return src
except Exception,e:
return str(e)
$BODY$
LANGUAGE 'plpythonu' VOLATILE
COST 100;

Weird. You seem to need both the try block and the overwrite of the
parameter to make it misbehave. I suspect this means we're doing
something a bit wrong in setting up the python variable for the
parameter. Unfortunately I don't know enough about python to go further
than that.

regards, tom lane

Not sure about the try block being related, I included it in my example
mostly because the example is a simplified version of some code I was
working on that had a try/except block.
I tried the function without the try block and it raised the same
exception (just uncaught):

CREATE OR REPLACE FUNCTION pyreplacenotry(src text, s text)
RETURNS text AS
$BODY$
src=src.replace(s,'')
return src
$BODY$
LANGUAGE 'plpythonu' VOLATILE
COST 100;
ALTER FUNCTION pyreplacenotry(text, text) OWNER TO dgardner;

gives me:
ERROR: PL/Python: PL/Python function "pyreplacenotry" failed
DETAIL: <type 'exceptions.UnboundLocalError'>: local variable 'src'
referenced before assignment

********** Error **********

ERROR: PL/Python: PL/Python function "pyreplacenotry" failed
SQL state: XX000
Detail: <type 'exceptions.UnboundLocalError'>: local variable 'src'
referenced before assignment

However this works:
CREATE OR REPLACE FUNCTION pyreplacenoreassign(src text, s text)
RETURNS text AS
$BODY$
return src.replace(s,'')
$BODY$
LANGUAGE 'plpythonu' VOLATILE
COST 100;
ALTER FUNCTION pyreplacenoreassign(text, text) OWNER TO dgardner;

Tom Lane wrote:

"David Gardner" <dgardner@creatureshop.com> writes:

CREATE OR REPLACE FUNCTION pyreplace(src text,s text)
RETURNS text AS
$BODY$
try:
src=src.replace(s,'')
return src
except Exception,e:
return str(e)
$BODY$
LANGUAGE 'plpythonu' VOLATILE
COST 100;

Weird. You seem to need both the try block and the overwrite of the
parameter to make it misbehave. I suspect this means we're doing
something a bit wrong in setting up the python variable for the
parameter. Unfortunately I don't know enough about python to go further
than that.

regards, tom lane

--
David Gardner
Pipeline Tools Programmer
Jim Henson Creature Shop
dgardner@creatureshop.com

On tor, 2009-12-03 at 14:46 -0800, David Gardner wrote:

Not sure about the try block being related, I included it in my
example mostly because the example is a simplified version of some
code I was working on that had a try/except block.
I tried the function without the try block and it raised the same
exception (just uncaught):

CREATE OR REPLACE FUNCTION pyreplacenotry(src text, s text)
RETURNS text AS
$BODY$
src=src.replace(s,'')
return src
$BODY$
LANGUAGE 'plpythonu' VOLATILE
COST 100;
ALTER FUNCTION pyreplacenotry(text, text) OWNER TO dgardner;

gives me:
ERROR: PL/Python: PL/Python function "pyreplacenotry" failed
DETAIL: <type 'exceptions.UnboundLocalError'>: local variable 'src'
referenced before assignment

What is going on internally is something like this:

src = 'xyz'

def pyreplacenotry():
src=src.replace('x', 'y')
return src

pyreplacenotry()

which fails with that same error. So you should not try to assign to
the parameters of a function.

Peter Eisentraut <peter_e@gmx.net> writes:

... So you should not try to assign to
the parameters of a function.

If it's allowed in normal Python functions, that definitely needs to be
documented. Better would be to fix it or at least throw a more
intelligible error ...

regards, tom lane

On tor, 2009-12-03 at 19:02 -0500, Tom Lane wrote:

Peter Eisentraut <peter_e@gmx.net> writes:

... So you should not try to assign to
the parameters of a function.

If it's allowed in normal Python functions, that definitely needs to be
documented. Better would be to fix it or at least throw a more
intelligible error ...

I have added documentation for it.