C++ exceptions get translated to Python OpenMMException class (#2672)

wrappers/python/simtk/openmm/__init__.py

@@ -30,3 +30,7 @@ if sys.platform == 'win32':
     os.environ['PATH'] = _path
     del _path
 __version__ = Platform.getOpenMMVersion()
+
+class OpenMMException(Exception):
+    """This is the class used for all exceptions thrown by the C++ library."""
+    pass

wrappers/python/src/swig_doxygen/swigInputConfig.py

@@ -18,6 +18,7 @@ SKIP_METHODS = [('State', 'getPositions'),
                 ('State', 'getForces'),
                 ('StateBuilder',),
                 ('Vec3',),
+                ('OpenMMException',),
                 ('AngleInfo',),
                 ('ApplyAndersenThermostatKernel',),
                 ('ApplyConstraintsKernel',),

wrappers/python/src/swig_doxygen/swig_lib/python/exceptions.i

@@ -3,7 +3,9 @@
     try {
         $action
     } catch (std::exception &e) {
-        PyErr_SetString(PyExc_Exception, const_cast<char*>(e.what()));
+        PyObject* mm = PyImport_AddModule("simtk.openmm");
+        PyObject* openmm_exception = PyObject_GetAttrString(mm, "OpenMMException");
+        PyErr_SetString(openmm_exception, const_cast<char*>(e.what()));
         return NULL;
     }
 }
@@ -14,7 +16,9 @@
         $action
     } catch (std::exception &e) {
         PyEval_RestoreThread(_savePythonThreadState);
-        PyErr_SetString(PyExc_Exception, const_cast<char*>(e.what()));
+        PyObject* mm = PyImport_AddModule("simtk.openmm");
+        PyObject* openmm_exception = PyObject_GetAttrString(mm, "OpenMMException");
+        PyErr_SetString(openmm_exception, const_cast<char*>(e.what()));
         return NULL;
     }
     PyEval_RestoreThread(_savePythonThreadState);
@@ -26,7 +30,9 @@
         $action
     } catch (std::exception &e) {
         PyEval_RestoreThread(_savePythonThreadState);
-        PyErr_SetString(PyExc_Exception, const_cast<char*>(e.what()));
+        PyObject* mm = PyImport_AddModule("simtk.openmm");
+        PyObject* openmm_exception = PyObject_GetAttrString(mm, "OpenMMException");
+        PyErr_SetString(openmm_exception, const_cast<char*>(e.what()));
         return NULL;
     }
     PyEval_RestoreThread(_savePythonThreadState);