char** to {'':('',)}

[Ignacio Vazquez-Abrams]

On Wed, 29 Aug 2001, Tim Peters wrote:

> [Ignacio Vazquez-Abrams]
> > I am using the following blecherous code to do a conversion from
> > char*s in the form "<a>=<b>" to the form {'<a>':(tuple of '<b>'s), ...}.
> > I'm sure that there's probably a more straightforward way out there.
> > Does anyone have any ideas as to how I can simplifiy this?
>
> Ya, write it in Python -- coding in C is a PITA.  If you need to do it in C
> for speed (whatever), don't be afraid of gotos!  The Python implementation
> has many examples of this, jumping to an error label at the end when things
> go wrong "in the middle".

Unfortunately I have even more pragmatic a reason for doing it in C than
speed; I get the char** for a library written in C, and some days it's just
NOT worth using the struct module.

And don't take this the wrong way, but I refuse to use goto. No, don't bother
arguing; there's no point.

> > ...
> >   PyObject *dict=NULL, *list=NULL;
> > ...
> >   i=0;
> >   while(PyDict_Next(dict, &i, &key, &val))
> >   {
> >     PyDict_SetItem(result, key, PyList_AsTuple(val));
> >   };
> >
> >   return result;
> > };
>
> It looks like you're letting dict leak in the normal case, and gotos help
> prevent mistakes like that too.

Yeah, I caught that one a couple of hours after posting.

> practicality-beats-purity-ly y'rs  - tim

Pfft! You don't know me very well, do you? ;)

> BTW, in cases like this:
>
>     val=PyString_FromString(equals+1);
>     if (val==NULL)
>     {
>       PyErr_SetString(MyError, "Something else most blecherous happened!");
>       Py_XDECREF(dict);
>       Py_XDECREF(result);
>       return NULL;
>     };
>
> PyString_FromString will already have set an appropriate exception
> explaining the difficulty, so it's more work *and* usually harmful to make
> up your own msg (proof:  just *read* your msg above <wink>).

Heh :) I just needed an error message so that I could be certain that I
wouldn't get that silly "No exception was set" message.

I've noticed two big holes in the Python/C API:

1) It doesn't say for all functions which ones set exceptions, and
2) It doesn't say for all functions whether or not they increment refcounts of
     objects passed to them, viz. PyDict_SetString().

-- 
Ignacio Vazquez-Abrams  <ignacio at openservices.net>