0.7.x: Show Cephes errors as Python warnings instead of fprintfing.

This changes cephes/mtherr.c to signal warnings via PyErr_WarnEx rather
than fprintf. (Though error printing is disabled by default, as previously.)

Backported: http://svn.scipy.org/svn/scipy/trunk@5514 d6536bca-fef9-0310-8506-e4c0a848fbcf
(cherry picked from commit 8ea62852f764d1719aa65ebe69684fa597c5c357)

scipy/special/_cephesmodule.c

@@ -6,6 +6,7 @@
  *  Copyright 1999  Travis E. Oliphant
  * Revisions 2002 (added functions from cdflib)
  */
+#include <stdarg.h>
 
 #include "Python.h"
 #include "numpy/arrayobject.h"
@@ -1050,6 +1051,23 @@ static void Cephes_InitOperators(PyObject *dictionary) {
 
 }
 
+static PyObject *scipy_special_SpecialFunctionWarning = NULL;
+
+void scipy_special_raise_warning(char *fmt, ...)
+{
+    NPY_ALLOW_C_API_DEF
+    char msg[1024];
+    va_list ap;
+
+    va_start(ap, fmt);
+    PyOS_vsnprintf(msg, 1024, fmt, ap);
+    va_end(ap);
+
+    NPY_ALLOW_C_API
+    PyErr_WarnEx(scipy_special_SpecialFunctionWarning, msg, 2);
+    NPY_DISABLE_C_API
+}
+
 static char errprint_doc[] = \
 "errprint({flag}) sets the error printing flag for special functions\n" \
 "    (from the cephesmodule). The output is the previous state.\n" \
@@ -1102,6 +1120,14 @@ PyMODINIT_FUNC init_cephes(void) {
   /* Load the cephes operators into the array module's namespace */
   Cephes_InitOperators(d);
 
+  /* Register and add the warning type object */
+  scipy_special_SpecialFunctionWarning = PyErr_NewException(
+      "scipy.special._cephes.SpecialFunctionWarning",
+      PyExc_RuntimeWarning,
+      NULL);
+  PyModule_AddObject(m, "SpecialFunctionWarning",
+                     scipy_special_SpecialFunctionWarning);
+
   /* Check for errors */
   if (PyErr_Occurred())
     Py_FatalError("can't initialize module _cephes");

scipy/special/cephes/mtherr.c

@@ -57,6 +57,7 @@ Direct inquiries to 30 Frost Street, Cambridge, MA 02140
 #include <stdio.h>
 #include "mconf.h"
 
+void scipy_special_raise_warning(char *fmt, ...);
 int scipy_special_print_error_messages = 0;
 
 int merror = 0;
@@ -66,42 +67,39 @@ int merror = 0;
  * in mconf.h.
  */
 static char *ermsg[8] = {
-"unknown",      /* error code 0 */
-"domain",       /* error code 1 */
-"singularity",  /* et seq.      */
-"overflow",
-"underflow",
-"total loss of precision",
-"partial loss of precision",
-"too many iterations"
+    "unknown",			/* error code 0 */
+    "domain",			/* error code 1 */
+    "singularity",		/* et seq.      */
+    "overflow",
+    "underflow",
+    "total loss of precision",
+    "partial loss of precision",
+    "too many iterations"
 };
 
 
-int mtherr( name, code )
-char *name;
-int code;
+int mtherr(char *name, int code)
 {
+    /* Display string passed by calling program,
+     * which is supposed to be the name of the
+     * function in which the error occurred:
+     */
 
-/* Display string passed by calling program,
- * which is supposed to be the name of the
- * function in which the error occurred:
- */
-
-/* Set global error message word */
-merror = code;
+    /* Set global error message word */
+    merror = code;
 
-/* Display error message defined
- * by the code argument.
- */
-if( (code <= 0) || (code >= 8) )
+    /* Display error message defined
+     * by the code argument.
+     */
+    if ((code <= 0) || (code >= 8))
 	code = 0;
-if (scipy_special_print_error_messages) {
-        printf( "\n%s ", name );
-        printf( "%s error\n", ermsg[code] );
-}
 
-/* Return to calling
- * program
- */
-return( 0 );
+    if (scipy_special_print_error_messages) {
+        scipy_special_raise_warning("%s: %s error", name, ermsg[code]);
+    }
+
+    /* Return to calling
+     * program
+     */
+    return (0);
 }