Re: [Numpy-discussion] Determine if numpy is installed from anextension

Feb. 3, 2010

      Just to imform that my approach works:

if (_import_array() < 0) {

   /* Clear the error state since we are handling the error. */
   PyErr_Clear();
   /* ... set up for the sans-numpy case. */
}
else {
   /* ... set up for the with-numpy case. */
}

It is based on Roberts idea to call PyImport_ImportModule("numpy"); and check if that succeededand clean up. In fact, _import_array() is doing this.
The code of _import_array() is in the header file __multiarray_api.h in the numpy folder of the distributed files:

static int
_import_array(void)
{
  int st;
  PyObject *numpy = PyImport_ImportModule("numpy.core.multiarray");
  PyObject *c_api = NULL;
  if (numpy == NULL) return -1;
  c_api = PyObject_GetAttrString(numpy, "_ARRAY_API");
  if (c_api == NULL) {Py_DECREF(numpy); return -1;}
  if (PyCObject_Check(c_api)) {
      PyArray_API = (void **)PyCObject_AsVoidPtr(c_api);
  }
  Py_DECREF(c_api);
  Py_DECREF(numpy);
  if (PyArray_API == NULL) return -1;
  /* Perform runtime check of C API version */
  if (NPY_VERSION != PyArray_GetNDArrayCVersion()) {
    PyErr_Format(PyExc_RuntimeError, "module compiled against "\
        "ABI version %x but this version of numpy is %x", \
        (int) NPY_VERSION, (int) PyArray_GetNDArrayCVersion());
    return -1;
  }
  if (NPY_FEATURE_VERSION > PyArray_GetNDArrayCFeatureVersion()) {
    PyErr_Format(PyExc_RuntimeError, "module compiled against "\
        "API version %x but this version of numpy is %x", \
        (int) NPY_FEATURE_VERSION, (int) PyArray_GetNDArrayCFeatureVersion());
    return -1;
  }

  /*
   * Perform runtime check of endianness and check it matches the one set by
   * the headers (npy_endian.h) as a safeguard
   */
  st = PyArray_GetEndianness();
  if (st == NPY_CPU_UNKNOWN_ENDIAN) {
    PyErr_Format(PyExc_RuntimeError, "FATAL: module compiled as unknown endian");
    return -1;
  }
#if NPY_BYTE_ORDER ==NPY_BIG_ENDIAN
  if (st != NPY_CPU_BIG) {
    PyErr_Format(PyExc_RuntimeError, "FATAL: module compiled as "\
        "big endian, but detected different endianness at runtime");
    return -1;
  }
#elif NPY_BYTE_ORDER == NPY_LITTLE_ENDIAN
  if (st != NPY_CPU_LITTLE) {
    PyErr_Format(PyExc_RuntimeError, "FATAL: module compiled as "\
        "little endian, but detected different endianness at runtime");
    return -1;
  }
#endif

  return 0;
}

As you can see, this routine is doing the same at the beginning with additional tests and the return value indicates if ok or not.

So I only had to call PyErr_Clear(); when it failes and the problem is solved.

Thanks for your input.

Peter 

From: Peter Notebaert 
Sent: Wednesday, February 03, 2010 16:57
To: Discussion of Numerical Python 
Subject: Re: [Numpy-discussion] Determine if numpy is installed from anextension

Ah, that is maybe the idea: 

if (_import_array() < 0) {

   /* Clear the error state since we are handling the error. */
   PyErr_Clear();
   /* ... set up for the sans-numpy case. */
}
else {
   /* ... set up for the with-numpy case. */
}

I did not call PyErr_Clear() when _import_array() < 0 and the error is probably still hanging and then given later.

I will try this this evening.

Thank you for the hints.

Peter

On Wed, Feb 3, 2010 at 4:22 PM, Robert Kern <robert.kern@gmail.com> wrote:

  On Wed, Feb 3, 2010 at 03:41, David Cournapeau <cournape@gmail.com> wrote:
...
On Wed, Feb 3, 2010 at 5:38 PM, Peter Notebaert <peno@telenet.be> wrote:
...
...
From an extension? How to import numpy from there and then test if that
succeeded and that without any annoying message if possible...
One obvious solution would be to simply call PyImport_Import, something like:
#include <Python.h>
PyMODINIT_FUNC initfoo(void)
{
       PyObject *m, *mod;
m = Py_InitModule("foo", NULL);
       if (m == NULL) {
               return;
       }
mod = PyImport_ImportModule("numpy");
       if (mod == NULL) {
               return;
       }
       Py_DECREF(mod);
Or rather, to recover from the failed import as the OP wants to do:

  mod = PyImport_ImportModule("numpy");
  if (mod == NULL) {

     /* Clear the error state since we are handling the error. */
     PyErr_Clear();
     /* ... set up for the sans-numpy case. */
  }
  else {
     Py_DECREF(mod);
     import_array();
     /* ... set up for the with-numpy case. */
  }

  --
  Robert Kern

  "I have come to believe that the whole world is an enigma, a harmless
  enigma that is made terrible by our own mad attempt to interpret it as
  though it had an underlying truth."
   -- Umberto Eco

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