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

The following bug has been logged online:

Bug reference:      5232
Logged by:          David Gardner
Email address:      dgardner@creatureshop.com
PostgreSQL version: 8.4.1
Operating system:   Debian, amd64
Description:        plpythonu s=s.op() raises an exception
Details:

If I create the following:
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;
ALTER FUNCTION pyreplace(src text,s text) OWNER TO dgardner;

Then:
SELECT * FROM pyreplace('this is a very long string','is');
                     pyreplace
---------------------------------------------------
 local variable 'src' referenced before assignment
(1 row)


However in python I can do:
def pyreplace(src,s):
    try:
        src=src.replace(s,'')
        return src
    except Exception,e:
        return str(e)

pyreplace('this is a very long string','is')
-----
produces:
'th  a very long string'

"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.