Re: SystemError: null argument to internal routine

On 03/03/11 20:52, Eric Snow wrote:
> I am trying to figure out the conditions under which I get that
> SystemError.  Here is a simple way that I found to reproduce the
> problem:
>
>>>> import psycopg2
>>>> psycopg2.__version__
> '2.3.2 (dt dec pq3 ext)'
>>>> conn = psycopg2.connect("...")
>>>> cur = conn.cursor()
>>>> cur.execute(";")
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> SystemError: null argument to internal routine
>
> I am getting the same exception during a call to copy_expert.  How would
> the data I pass in there trigger the same exception as when I pass a
> single semicolon?  I am guessing that it does not even make it over the
> wire to the postgres server when the exception is raised.  Thanks.

Aaah, that rings a bell. I was getting the same error with txpostgres
and even once found out why, but forgot, and now I remembered.

I believe that the problem is in pqpath.c, in pq_fetch. There's a switch
statement there that checks the result of PQresultStatus and does not
take PGRES_EMPTY_QUERY into consideration.

The code that jumps to the default: label, which leads it to pq_raise.
Towards the end there's a

if (code != NULL)
   exc = exception_from_sqlstate(code);

which AFAIR never gets executed, because code *is* NULL. And then it
hits psyco_set_error with a NULL exception, this leads to the "NULL
argument to internal routine" error.

I might have messed up some details, but I'm pretty sure the problem is
not handling PGRES_EMPTY_QUERY correctly.

Cheers,
Jan