handle return error of trexio_open in the Python API

python/test/test_api.py

@@ -49,7 +49,7 @@ nucleus_num = 12
 try:
     trexio.write_nucleus_num(test_file, -100)
 except trexio.Error:
-    print("Writing negative nucleus_num: checked.")
+    print("Raise error for an attempt to write negative nucleus_num: checked.")
 
 # write nucleus_num in the file
 try:
@@ -60,7 +60,7 @@ except:
 try:
     trexio.write_nucleus_num(test_file, nucleus_num*2)
 except trexio.Error:
-    print("Attempt to overwrite nucleus_num: checked.")
+    print("Raise error for an attempt to overwrite nucleus_num: checked.")
 
 # initialize charge arrays as a list and convert it to numpy array
 charges = [6., 6., 6., 6., 6., 6., 1., 1., 1., 1., 1., 1.]
@@ -199,7 +199,7 @@ assert rpoint_group==point_group
 if trexio.has_mo_num(test_file2):
     rmo_num = trexio.read_mo_num(test_file2)
 else:
-    print("Not reading the non-existing variable mo_num.")
+    print("Pass on reading the non-existing variable mo_num: checked")
 
 # close TREXIO file
 #trexio.close(test_file2)
@@ -215,3 +215,16 @@ except:
 
 #==========================================================#
 
+#==========================================================#
+#======= OPEN NON-EXISTING FILE TO TEST TREXIO.OPEN =======#
+#==========================================================#
+
+try:
+    void_file = trexio.File('non_existing.file', 'r', TEST_TREXIO_BACKEND)
+except trexio.Error as e:
+    if e.error == trexio.TREXIO_OPEN_ERROR:
+        print("Opening non-existing file returns TREXIO_OPEN_ERROR: checked")
+    else:
+        raise ValueError("[DEV]: error handling of trexio_open function has changed; check the consistency")
+
+#==========================================================#

src/pytrexio.i

@@ -37,6 +37,7 @@
 %apply int *OUTPUT { int64_t* const num};
 %apply float *OUTPUT { float* const num};
 %apply float *OUTPUT { double* const num};
+%apply int *OUTPUT { trexio_exit_code* const rc_open};
 
 /* Does not work for arrays (SIGSEGV) */
 

src/templates_front/templator_front.org

@@ -911,11 +911,22 @@ def open(file_name: str, mode: str, back_end: int):
     >>> trex_file = tr_open("example.h5", "w", TREXIO_HDF5)
     """
 
+    # The new trexio_open function is capable of returning error code which SWIG can append to the output trexio_s file struct
+    # However, if trexio_s* == NULL, then SWIG returns only an error code rc_open instead of a list [trexio_s, rc_open]
+    # Thus, the following try/except sequence is needed
     try:
-        trexio_file = pytr.trexio_open(file_name, mode, back_end)
-        assert trexio_file is not None
+        return_obj = pytr.trexio_open(file_name, mode, back_end)
+        assert return_obj is not None
+        if isinstance(return_obj, int):
+            raise Error(return_obj)
+        else:
+            rc_open = return_obj[1]
+            # this is a sanity check in case the code evolves and SWIG issue is patched
+            if rc_open == TREXIO_SUCCESS:
+                trexio_file = return_obj[0]
+                assert trexio_file is not None
     except AssertionError:
-        raise Exception(f"Could not open TREXIO file {file_name} using trexio_open function. Please make sure that there are no typos in the file name.")
+        raise Exception(f"Could not open TREXIO file {file_name} using trexio_open function. The return value is None (NULL pointer).")
 
     return trexio_file
    #+end_src