[GNC-dev] Problems with python 3 and the gnucash python bindings.

[John Ralls]

> On Jul 12, 2018, at 7:23 AM, Derek Atkins <warlord at mit.edu> wrote:
> 
> John Ralls <jralls at ceridwen.us> writes:
> 
>>> PS. Another solution would be to force byte string only arguments for
>>> python 3 using a SWIG define SWIG_PYTHON_STRICT_BYTE_CHAR.
>>> 
>>> This would require a major re-write of the gnucash_core.py to perform the
>>> unicode<->byte transformations.
>> 
>> ISTM it would be better to fix qof_query. It shouldn't be assuming
>> that just because it has typedeffed const char* to "QofIdTypeConst"
>> that it will necessarily get a statically allocated char* that is safe
>> to keep. There's absolutely nothing preventing it from being a stack
>> or heap object (stack is more likely in C, as in
>>  QofIdTypeConst type = "book"; 
>>  qof_query_search_for(query, type);
>> ) that will cause the same crash.
> 
> I disagree -- the API specification is clear that it will store the
> pointer, so callers need to know this.
> 

Where? The Doxygen comment is:

/** Set the object type to be searched for.  The results of
 *  performing the query will be a list of this obj_type.
 */
void qof_query_search_for (QofQuery *query, QofIdTypeConst obj_type);

Not only silent about storing a pointer, it even hides the fact that it’s a pointer at all. One has to go look at the typedef for QofIdTypeConst in qofid.h to see that it’s a const char *. 

> When it moves to C++ you can just use std::string.  :)

An enum would be safer, faster, smaller, more intuitive, and wouldn’t break swig.

Regards,
John Ralls 

> 
>> There are probably other cases where someone has made the same bad
>> assumption and stored an unduplicated char*, though I hope none quite
>> so egregious.
>> 
>> Please file a bug: https://wiki.gnucash.org/wiki/Bugzilla
>> 
>> Regards,
>> John Ralls
> 
> -derek
> -- 
>       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
>       Member, MIT Student Information Processing Board  (SIPB)
>       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
>       warlord at MIT.EDU                        PGP key available