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Thread: PLPython and named arguments

PLPython and named arguments

From
"Andrey Avakimov"
Date:
<p><span style="font-family: 'Courier New','Courier';">Hello</span><p><span style="font-family: 'Courier
New','Courier';">Myquestion is about plpython behavior. In some cases procedure ignores named arguments and raises an
errorlike:</span><p><span style="font-family: 'Courier New','Courier';">UnboundLocalError: local variable 'arg_from'
referencedbefore assignment</span><p><p><span style="font-family: 'Courier New','Courier';">This can be solved by using
suchcode:</span><p><span style="font-family: 'Courier New','Courier';">arg_from, arg_to = args</span><p><span
style="font-family:'Courier New','Courier';">But the reasons of such behavior are still unclear.<br /></span><p><span
style="font-family:'Courier New','Courier';">Does anyone faced this thing? </span><p><span style="font-family: 'Courier
New','Courier';">Iwill gladly provide any further information if needed.</span><p><p><span style="font-family: 'Courier
New','Courier';">BestRegards,</span><br /><span style="font-family: 'Courier New','Courier';">Andrew</span>

Re: PLPython and named arguments

From
Tom Lane
Date:
"Andrey Avakimov" <aquarius1993@rambler.ru> writes:
> My question is about plpython behavior. In some cases procedure ignores named
> arguments and raises an error like:
> UnboundLocalError: local variable 'arg_from' referenced before assignment

Let's see an example?
        regards, tom lane

Re: PLPython and named arguments

From
Adrian Klaver
Date:
On 10/04/2016 05:20 AM, Andrey Avakimov wrote:
> Hello
>
> My question is about plpython behavior. In some cases procedure ignores
> named arguments and raises an error like:
>
> UnboundLocalError: local variable 'arg_from' referenced before assignment

Because of this?:

https://www.postgresql.org/docs/9.6/static/plpython-funcs.html
"
The arguments are set as global variables. Because of the scoping rules 
of Python, this has the subtle consequence that an argument variable 
cannot be reassigned inside the function to the value of an expression 
that involves the variable name itself, unless the variable is 
redeclared as global in the block. For example, the following won't work:

CREATE FUNCTION pystrip(x text)  RETURNS text
AS $$  x = x.strip()  # error  return x
$$ LANGUAGE plpythonu;

because assigning to x makes x a local variable for the entire block, 
and so the x on the right-hand side of the assignment refers to a 
not-yet-assigned local variable x, not the PL/Python function parameter. 
Using the global statement, this can be made to work:

CREATE FUNCTION pystrip(x text)  RETURNS text
AS $$  global x  x = x.strip()  # ok now  return x
$$ LANGUAGE plpythonu;

But it is advisable not to rely on this implementation detail of 
PL/Python. It is better to treat the function parameters as read-only."


So:

test=# select * from pystrip('test  ');
ERROR:  UnboundLocalError: local variable 'x' referenced before assignment
CONTEXT:  Traceback (most recent call last):  PL/Python function "pystrip", line 2, in <module>    x = x.strip()  #
error
PL/Python function "pystrip"



>
> This can be solved by using such code:
>
> arg_from, arg_to = args
>
> But the reasons of such behavior are still unclear.
>
> Does anyone faced this thing?
>
> I will gladly provide any further information if needed.
>
> Best Regards,
> Andrew
>


-- 
Adrian Klaver
adrian.klaver@aklaver.com

Re: PLPython and named arguments

From
"Andrey Avakimov"
Date:
OMG... I feel ashamed that I missed that part of the documentation.
Thank you

Best Regards,
Andrew

> 04.10.2016, 16:22:55 пользователь Adrian Klaver (adrian.klaver@aklaver.com) написал:
>
> On 10/04/2016 05:20 AM, Andrey Avakimov wrote:
> > Hello
> >
> > My question is about plpython behavior. In some cases procedure ignores
> > named arguments and raises an error like:
> >
> > UnboundLocalError: local variable 'arg_from' referenced before assignment
>
> Because of this?:
>
> https://www.postgresql.org/docs/9.6/static/plpython-funcs.html
> "
> The arguments are set as global variables. Because of the scoping rules
> of Python, this has the subtle consequence that an argument variable
> cannot be reassigned inside the function to the value of an expression
> that involves the variable name itself, unless the variable is
> redeclared as global in the block. For example, the following won't work:
>
> CREATE FUNCTION pystrip(x text)
>       RETURNS text
> AS $$
>       x = x.strip()    # error
>       return x
> $$ LANGUAGE plpythonu;
>
> because assigning to x makes x a local variable for the entire block,
> and so the x on the right-hand side of the assignment refers to a
> not-yet-assigned local variable x, not the PL/Python function parameter.
> Using the global statement, this can be made to work:
>
> CREATE FUNCTION pystrip(x text)
>       RETURNS text
> AS $$
>       global x
>       x = x.strip()    # ok now
>       return x
> $$ LANGUAGE plpythonu;
>
> But it is advisable not to rely on this implementation detail of
> PL/Python. It is better to treat the function parameters as read-only."
>
> So:
>
> test=# select * from pystrip('test    ');
> ERROR:    UnboundLocalError: local variable 'x' referenced before assignment
> CONTEXT:    Traceback (most recent call last):
>       PL/Python function "pystrip", line 2, in <module>
>           x = x.strip()    # error
> PL/Python function "pystrip"
>
> >
> > This can be solved by using such code:
> >
> > arg_from, arg_to = args
> >
> > But the reasons of such behavior are still unclear.
> >
> > Does anyone faced this thing?
> >
> > I will gladly provide any further information if needed.
> >
> > Best Regards,
> > Andrew
> >
>
> --
> Adrian Klaver
> adrian.klaver@aklaver.com
>
> --
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