python3: Handle differences in module initialization

As described here:

http://python3porting.com/cextensions.html#module-initialization

Use macros to mask the differences in the return value type of the
module init function, and invocation of either Py_InitModule3 or
PyModule_Create.

Signed-off-by: Andy Grover <agrover@redhat.com>

Author: Andy Grover

python-ethtool/ethtool.c

@@ -899,19 +899,34 @@ static struct PyMethodDef PyEthModuleMethods[] = {
 	{	.ml_name = NULL, },
 };
 
+#if PY_MAJOR_VERSION >= 3
+  #define MOD_ERROR_VAL NULL
+  #define MOD_SUCCESS_VAL(val) val
+  #define MOD_INIT(name) PyMODINIT_FUNC PyInit_##name(void)
+  #define MOD_DEF(ob, name, doc, methods) \
+          static struct PyModuleDef moduledef = { \
+            PyModuleDef_HEAD_INIT, name, doc, -1, methods, }; \
+          ob = PyModule_Create(&moduledef);
+#else
+  #define MOD_ERROR_VAL
+  #define MOD_SUCCESS_VAL(val)
+  #define MOD_INIT(name) void init##name(void)
+  #define MOD_DEF(ob, name, doc, methods) \
+          ob = Py_InitModule3(name, methods, doc);
+#endif
 
-PyMODINIT_FUNC initethtool(void)
+MOD_INIT(ethtool)
 {
 	PyObject *m;
-	m = Py_InitModule3("ethtool", PyEthModuleMethods, "Python ethtool module");
+	MOD_DEF(m, "ethtool", "Python ethtool module", PyEthModuleMethods);
 
 	// Prepare the ethtool.etherinfo class
 	if (PyType_Ready(&PyEtherInfo_Type) < 0)
-		return;
+		return MOD_ERROR_VAL;
 
 	// Prepare the ethtool IPv6 and IPv4 address types
 	if (PyType_Ready(&ethtool_netlink_ip_address_Type))
-		return;
+		return MOD_ERROR_VAL;
 
 	// Setup constants
 	PyModule_AddIntConstant(m, "IFF_UP", IFF_UP);			/* Interface is up. */
@@ -933,6 +948,8 @@ PyMODINIT_FUNC initethtool(void)
 	PyModule_AddIntConstant(m, "AF_INET", AF_INET);                 /* IPv4 interface */
 	PyModule_AddIntConstant(m, "AF_INET6", AF_INET6);               /* IPv6 interface */
 	PyModule_AddStringConstant(m, "version", "python-ethtool v" VERSION);
+
+	return MOD_SUCCESS_VAL(m);
 }