Adding symbolic constants with hex values to Python extension module

Question

I have a few values defined as symbolic constants in my header file:

#define NONE 0x00
#define SYM  0x11
#define SEG  0x43
...

The names of these values represent a certain type of data.

Now in my current implementation of my module I put all these symbolic links into an array

static unsigned char TYPES[] = { NONE, SYM, SEG, ...}

And add the positions of the types in the array as int constants in the module.

PyMODINIT_FUNC initShell(void)
{
  PyObject *m;

  m=  Py_InitModule3("Sample", sample_Methods,"Sample Modules");
  if (m == NULL)
      return;
 ... 

  PyModule_AddIntConstant(m, "NONE", 0);
  PyModule_AddIntConstant(m, "SYM", 1);
  PyModule_AddIntConstant(m, "SEG", 2);
...
}

And when calling functions I have to do something like :

static PyObject *py_samplefunction(PyObject *self, PyObject *args, PyObject *kwargs) {

int type;
  if (!PyArg_ParseTuple(args,kwargs,"i",&type)
      return NULL;

 int retc;
 retc = sample_function(TYPES[type]);
 return Py_BuildValue("i", retc);
}

I'm not very happy with this hack and I think it is very prone to errors and so I'm basically looking for a solution which eliminates the array and allows for direct use of the constants in a function call. Any tips?

Edit

Using PyModule_AddIntMacro(m, SEG); and calling sample function as such, solves it:

static PyObject *py_samplefunction(PyObject *self, PyObject *args, PyObject *kwargs) {

int type;
  if (!PyArg_ParseTuple(args,kwargs,"i",&type)
      return NULL;

 int retc;
 retc = sample_function((unsigned char) type);
 return Py_BuildValue("i", retc);
}

WaffleSouffle · Accepted Answer · 2014-05-21 16:02:25Z

2

Why not just add the constants to the module ?

PyModule_AddIntMacro(m, SYM);

answered May 21, 2014 at 16:02

WaffleSouffle

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2 Comments

plover Over a year ago

Yes I tried that as well and when I do I get errors when I call the function with the constant. Perhaps I'm reading it in wrong, but I just can't spot the error

plover Over a year ago

I realized my error was that I forgot to cast the int constant to a unsigned char. That solved it

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