ImportError needs attributes for module and file name

Objects/exceptions.c

 /*
  * New exceptions.c written in Iceland by Richard Jones and Georg Brandl.
  *
  * Thanks go to Tim Peters and Michael Hudson for debugging.
  */
 
 #define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include "structmember.h"
 #include "osdefs.h"
@@ skipping 529 matching lines @@
 /*
  *    KeyboardInterrupt extends BaseException
  */
 SimpleExtendsException(PyExc_BaseException, KeyboardInterrupt,
                        "Program interrupted by user.");
 
 
 /*
  *    ImportError extends Exception
  */
-SimpleExtendsException(PyExc_Exception, ImportError,
-          "Import can't find module, or can't find name in module.");
 
+static int
+ImportError_init(PyImportErrorObject *self, PyObject *args, PyObject *kwds)
+{
+    PyObject *msg = NULL;
+    PyObject *module_name = NULL;
+        
+    if (kwds){
+        module_name = PyDict_GetItemString(kwds, "module_name");
+        if (module_name){
+            Py_CLEAR(self->module_name);       /* replacing */
+            self->module_name = module_name;
+            Py_INCREF(self->module_name);
+            if (PyDict_DelItemString(kwds, "module_name"))
+                return -1;
+        }
+    }
+    
+    if (BaseException_init((PyBaseExceptionObject *)self, args, kwds) == -1)
+        return -1;
+    if (PyTuple_GET_SIZE(args) != 1)
+        return 0;
+    if (!PyArg_UnpackTuple(args, "ImportError", 1, 1, &msg)) 
+        return -1;
+
+    Py_CLEAR(self->msg);          /* replacing */
+    self->msg = msg;
+    Py_INCREF(self->msg);
+
+    return 0;
+}
+
+static int
+ImportError_clear(PyImportErrorObject *self)
+{
+    Py_CLEAR(self->msg);
+    Py_CLEAR(self->module_name);
+    return BaseException_clear((PyBaseExceptionObject *)self);
+}
+
+static void
+ImportError_dealloc(PyImportErrorObject *self)
+{
+    _PyObject_GC_UNTRACK(self);
+    ImportError_clear(self);
+    Py_TYPE(self)->tp_free((PyObject *)self);
+}
+
+static int
+ImportError_traverse(PyImportErrorObject *self, visitproc visit, void *arg)
+{
+    Py_VISIT(self->msg);
+    Py_VISIT(self->module_name);
+    return BaseException_traverse((PyBaseExceptionObject *)self, visit, arg);
+}
+
+static PyObject *
+ImportError_str(PyImportErrorObject *self)
+{
+    if (self->msg) {
+        Py_INCREF(self->msg);
+        return self->msg;
+    }
+    else
+        return BaseException_str((PyBaseExceptionObject *)self);
+}
+
+static PyMemberDef ImportError_members[] = {
+    {"msg", T_OBJECT, offsetof(PyImportErrorObject, msg), 0,
+        PyDoc_STR("exception message")},
+    {"module_name", T_OBJECT, offsetof(PyImportErrorObject, module_name), 0,
+        PyDoc_STR("exception module_name")},
+    {NULL}  /* Sentinel */
+};
+
+static PyMethodDef ImportError_methods[] = {
+    {NULL}
+};
+
+ComplexExtendsException(PyExc_Exception, ImportError,
+                        ImportError, ImportError_dealloc,
+                        ImportError_methods, ImportError_members,
+                        ImportError_str,
+                        "Import can't find module, or can't find name in "
+                        "module.");
 
 /*
  *    EnvironmentError extends Exception
  */
 
 /* Where a function has a single filename, such as open() or some
  * of the os module functions, PyErr_SetFromErrnoWithFilename() is
  * called, giving a third argument which is the filename.  But, so
  * that old code using in-place unpacking doesn't break, e.g.:
  *
@@ skipping 1555 matching lines @@
 
     Py_DECREF(bltinmod);
 }
 
 void
 _PyExc_Fini(void)
 {
     Py_CLEAR(PyExc_RecursionErrorInst);
     free_preallocated_memerrors();
 }