Support both Python 2 and Python 3 in Python extension example. (#2495)

samples/python_extension/README.md

@@ -17,13 +17,13 @@ To build and run the sample do the following:
 *   On macOS copy Kotlin binary to extension's directory and change install name with
     `install_name_tool` tool, i.e.
     ```
-    sudo cp libserver.dylib  /Library/Python/2.7/site-packages/
+    sudo cp ./build/libserver.dylib  /Library/Python/2.7/site-packages/
     sudo install_name_tool /Library/Python/2.7/site-packages/kotlin_bridge.so \
           -change libserver.dylib @loader_path/libserver.dylib
     ```
 *   On Linux copy Kotlin binary in some place where libraries could be loaded from, i.e.
     ```
-    cp libserver.so /usr/local/lib/
+    cp ./build/libserver.so /usr/local/lib/
     ldconfig
     ```
     or modify dynamic loader search path with

samples/python_extension/build.sh

@@ -11,6 +11,7 @@ fi
 KONAN_USER_DIR=${KONAN_DATA_DIR:-"$HOME/.konan"}
 KONAN_DEPS="$KONAN_USER_DIR/dependencies"
 
+# python3 shall work as well.
 PYTHON=python
 
 mkdir -p $DIR/build

samples/python_extension/src/main/c/kotlin_bridge.c

@@ -108,6 +108,38 @@ static PyMethodDef kotlin_bridge_funcs[] = {
    { NULL }
 };
 
+#if PY_MAJOR_VERSION >= 3
+
+struct module_state {
+  server_kref_demo_Server server;
+};
+
+static int kotlin_bridge_traverse(PyObject *m, visitproc visit, void *arg) {
+    return 0;
+}
+
+static int kotlin_bridge_clear(PyObject *m) {
+    return 0;
+}
+
+static struct PyModuleDef moduledef = {
+        PyModuleDef_HEAD_INIT,
+        "kotlin_bridge",
+        NULL,
+        sizeof(struct module_state),
+        kotlin_bridge_funcs,
+        NULL,
+        kotlin_bridge_traverse,
+        kotlin_bridge_clear,
+        NULL
+};
+
+PyMODINIT_FUNC PyInit_kotlin_bridge(void) {
+   PyObject *module = PyModule_Create(&moduledef);
+   return module;
+}
+#else
 void initkotlin_bridge(void) {
    Py_InitModule3("kotlin_bridge", kotlin_bridge_funcs, "Kotlin/Native example module");
 }
+#endif

samples/python_extension/src/main/python/main.py

@@ -9,13 +9,13 @@ import kotlin_bridge
 session = kotlin_bridge.open_session(239, 'konan')
 
 message = kotlin_bridge.greet_server(session)
-print "Greet '%s'" % (message)
+print("Greet '{}'".format(message))
 
 message = kotlin_bridge.concat_server(session, "Coding", "fun")
-print "Concat '%s'" % (message)
+print("Concat '{}'".format(message))
 
 message = kotlin_bridge.add_server(session, 1, 60)
-print "Sum '%d'" % (message)
+print("Sum '{}'".format(message))
 
 
 kotlin_bridge.close_session(session)