PyArg_Parse vs PyArg_ParseTuple

Ignacio Vazquez-Abrams ignacio at openservices.net
Wed Oct 17 03:42:04 CEST 2001


On Wed, 17 Oct 2001, David Brady wrote:

> Hello,
>
> I'm new to Python, and I've searched the archives for more info but can't
> seem to find the info I need.  I am having trouble using PyArg_ParseTuple().
>   Here is the python code I'm embedding:
>
> # TestModule.py
> def NumberFunction(x):
> 	return x+1
>
> As you see, it's not too complex.  :-)  This is just a proof of concept I'm
> working on to prove it can be done.
>
> Here is the code I'm trying to embed it in.  Note: this is C++, does that
> make a difference in this case?
>
> // TestEmbed.cpp
> #include <stdio.h>
> #include <Python.h>
>
> void main(void)
> {
> 	long val = 7;
> 	PyObject *pmod, *pfunc, *pargs, *pstr;
>
> 	PyInitialize();
> 	printf( "Processing data: %ld\n", val );
>
> 	pmod = PyImport_ImportModule( "TestModule" );
> 	pfunc = PyObject_GetAttrString( pmod, "NumberFunction" );
>
> 	pargs = Py_BuildValue( "(l)", val );
> 	pstr = PyEval_CallObject( pfunc, pargs );
>
> 	// *** This code works ***
> 	PyArg_Parse( pstr, "l", &val );
>
> 	// *** This code does NOT work ***
> 	//PyArg_ParseTuple( pstr, "l", &val );
>
> 	printf( "Val returned was %d\n", val );
> }
>
>
> If I use the ParseTuple version, the code appears to run fine, but val is
> unchanged.  I've tried using "(l)" as the string but I'm grasping at straws
> here.
>
> I read in the documentatian that PyArg_Parse() is deprecated, so I would
> like to get this working correctly.

You're misunderstanding what PyArg_Parse() and PyArg_ParseTuple() are used
for. They are used for when a C function is called by a Python program, not
the other way around. In your case you should probably be using one of the
PyInt_As*() or PyLong_As*() functions.

Also, a C signed long on a 32-bit machine translates into a Python Integer, so
you can just as easily use "(i)" in Py_BuildValue().

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

   "As far as I can tell / It doesn't matter who you are /
    If you can believe there's something worth fighting for."
       - "Parade", Garbage





More information about the Python-list mailing list