Python external_runtime example fixup

- Modify example to actually use the external runtime in example.cxx.
- Correct formatting of files.
- Add exception handling.
- Rename two main classes in example for better clarity.

This commit fixes the previous commit so that the example now correctly
tests the commmit prior to it.

Note that -builtin is not run as it does not work (seg faults - needs
investigation).

Issue #3067

Examples/python/external_runtime/example.cxx

@@ -1,9 +1,29 @@
+/* File : example.cxx */
+
 #include <Python.h>
-#include "swig_runtime.hxx"
+#include <stdio.h>
 #include "example.h"
 
-Function::Function(PyObject * pyCallable)
-: pyObj_(pyCallable), meshValue_(0)
-{
-  // stuff happens in the typemap of PyObject * pyCallable
+#include "swig_runtime.hxx"
+
+MeshCaller::MeshCaller(PyObject *pyCallable) : pyObj_(pyCallable) {
+  if (pyObj_) {
+    PyObject *pyMesh = PyObject_CallMethod(pyObj_, const_cast<char *>("mesh"), const_cast<char *>("()"));
+    if (!pyMesh)
+      throw std::runtime_error("null pyMesh");
+    void *ptr = 0;
+
+    // Use SWIG_ConvertPtr and SWIG_TypeQuery in the SWIG external runtime
+    if (SWIG_IsOK(SWIG_ConvertPtr(pyMesh, &ptr, SWIG_TypeQuery("Mesh *"), 0))) {
+      Mesh *mesh = reinterpret_cast<Mesh *>(ptr);
+      if (!mesh)
+        throw std::runtime_error("null mesh");
+      const int value = mesh->value();
+      std::cout << "value = "<<value<<std::endl;
+      if (value != 42)
+        throw std::runtime_error("wrong value");
+    } else {
+      throw std::runtime_error("SWIG_ConvertPtr failed");
+    }
+  }
 }

Examples/python/external_runtime/example.h

@@ -3,22 +3,15 @@
 #include <iostream>
 #include "Python.h"
 
-class Mesh
-{
+class Mesh {
+  int value_;
 public:
-	Mesh(const int value = 0)
-	: value_(value) {}
-	int value() { return value_;}
-private:
-	int value_;
+  Mesh(const int value = 0) : value_(value) {}
+  int value() { return value_; }
 };
 
-class Function
-{
+class MeshCaller {
+  PyObject *pyObj_;
 public:
-	explicit Function(PyObject * pyCallable = 0);
-	int meshValue() { return meshValue_;}	int meshValue_;
-
-private:
-	PyObject * pyObj_;
+  explicit MeshCaller(PyObject *pyCallable = 0);
 };

Examples/python/external_runtime/example.i

@@ -1,30 +1,13 @@
 /* File : example.i */
 %module(docstring="external runtime") example
+
 %{
 #include "example.h"
 %}
 
-%typemap(in) PyObject * pyCallable
-{
-  if ($input)
-  {
-    PyObject * pyMesh = PyObject_CallMethod($input, const_cast<char *>("mesh"), const_cast<char *>("()"));
-    if (!pyMesh)
-      throw std::runtime_error("null pyMesh");
-    void * ptr = 0;
-    if (SWIG_IsOK(SWIG_ConvertPtr(pyMesh, &ptr, SWIG_TypeQuery("Mesh *"), 0)))
-    {
-      Mesh *mesh = reinterpret_cast< Mesh * >(ptr);
-      if (!mesh)
-        throw std::runtime_error("null mesh");
-      const int value = mesh->value();
-      std::cout << "value="<<value<<std::endl;
-      if (value != 42)
-        throw std::runtime_error("wrong value");
-    }
-  }
-}
-
+// Exception handling
+%include <std_except.i>
+%catches(std::runtime_error) MeshCaller::MeshCaller;
 
 %include "example.h"
 

Examples/python/external_runtime/runme.py

@@ -5,18 +5,16 @@
 import example
 
 
-class PyFunction(object):
+class MeshHolder(object):
     def __init__(self):
         self.__mesh = example.Mesh(42)
     def mesh(self):
         return self.__mesh
 
-if not example.is_python_builtin():
-    obj = PyFunction()
-    f = example.Function(obj)
-    print('OK')
+if example.is_python_builtin():
+    print("SWIG external runtime and builtin not currently working")
+else:
+    obj = MeshHolder()
+    f = example.MeshCaller(obj)
 
-# All done.
-
-print("")
-print("python exit")
+print("All done")