Avoid silent crashing of TMatrixInterpolator.__cinit__()

Former-commit-id: fb6bfc9f52b8d0dadf89c93835360bca54cb66c9

qpms/qpms_c.pyx

@@ -1134,6 +1134,8 @@ cdef class TMatrixInterpolator:
 
     def __cinit__(self, filename, BaseSpec bspec,  *args, **kwargs):
         '''Creates a T-matrix interpolator object from a scuff-tmatrix output'''
+        global qpms_load_scuff_tmatrix_crash_on_failure
+        qpms_load_scuff_tmatrix_crash_on_failure = False
         self.spec = bspec
         cdef char * cpath = make_c_string(filename)
         if QPMS_SUCCESS != qpms_load_scuff_tmatrix(cpath, self.spec.rawpointer(),

qpms/qpms_cdefs.pxd

@@ -276,6 +276,7 @@ cdef extern from "gsl/gsl_interp.h":
     # ^^^ These are probably the only relevant ones.
 
 cdef extern from "tmatrices.h":
+    bint qpms_load_scuff_tmatrix_crash_on_failure
     struct qpms_tmatrix_interpolator_t:
         const qpms_vswf_set_spec_t *bspec
     struct qpms_permittivity_interpolator_t:

qpms/tmatrices.c

@@ -18,6 +18,7 @@
 #include "tmatrices.h"
 #include "qpms_specfunc.h"
 #include "normalisation.h"
+#include <errno.h>
 
 #define HBAR (1.05457162825e-34)
 #define ELECTRONVOLT (1.602176487e-19)
@@ -443,6 +444,8 @@ qpms_errno_t qpms_read_scuff_tmatrix(
   return QPMS_SUCCESS;
 }
 
+bool qpms_load_scuff_tmatrix_crash_on_failure = true;
+
 qpms_errno_t qpms_load_scuff_tmatrix(
     const char *path, ///< file path
     const qpms_vswf_set_spec_t * bs, ///< VSWF set spec
@@ -453,9 +456,11 @@ qpms_errno_t qpms_load_scuff_tmatrix(
     complex double ** const tmdata
     ) {
   FILE *f = fopen(path, "r");
-  if (!f)
-    qpms_pr_error_at_line(__FILE__, __LINE__, __func__,
-        "Could not open T-matrix file %s", path); 
+  if (!f) 
+    if (qpms_load_scuff_tmatrix_crash_on_failure)
+      qpms_pr_error_at_line(__FILE__, __LINE__, __func__,
+          "Could not open T-matrix file %s", path); 
+    else return errno;
   qpms_errno_t retval = 
     qpms_read_scuff_tmatrix(f, bs, n, freqs, freqs_su, tmatrices_array, tmdata);
 

qpms/tmatrices.h

@@ -139,6 +139,17 @@ qpms_errno_t qpms_load_scuff_tmatrix(
 		complex double **tmdata ///< The T-matrices raw contents
 		);
 
+/// Tells whether qpms_load_scuff_tmatrix should crash if fopen() fails.
+/** If true (default), the function causes the program
+ * die e.g. when the tmatrix file
+ * does not exists.
+ *
+ * If false, it does nothing and returns an appropriate error value instead.
+ * This is desirable e.g. when used in Python (so that proper exception can
+ * be thrown).
+ */
+extern bool qpms_load_scuff_tmatrix_crash_on_failure;
+
 /// Loads a scuff-tmatrix generated file.
 /** A simple wrapper over qpms_read_scuff_tmatrix() that needs a 
  * path instead of open FILE.