Testcase for testing __new__ override Python 3.6 fix

Issue #1357

CHANGES.current

@@ -7,6 +7,11 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.0.0 (in progress)
 ===========================
 
+2018-12-20: chlandsi
+            [Python] #1357. Fix overriding __new__ in Python 3.6.
+
+            Fixes SystemError: Objects/tupleobject.c:81: bad argument to internal function"
+
 2018-10-29: AlexanderGabriel
 	    [PHP] The following PHP7 reserved keywords are now only renamed by
 	    SWIG when used as function names in the API being wrapper:

Examples/test-suite/python/python_pythoncode_runme.py

@@ -3,3 +3,7 @@ import python_pythoncode
 # No need to actually do anything, this is a regression test for a bug which
 # caused an invalid python_pythoncode.py to be generated, so if we can import
 # it the bug is still fixed.
+
+# A later test enhancement checking __new__ requires some code...
+f = python_pythoncode.get_foo()
+f = python_pythoncode.Foo()

Examples/test-suite/python_pythoncode.i

@@ -29,3 +29,33 @@ struct TYPE2 {
 struct TYPE { };
 struct TYPE2 { };
 %}
+
+
+// Overriding __new__ test: https://github.com/swig/swig/pull/1357
+%inline %{
+class Foo {
+  public:
+    virtual ~Foo() {}
+    Foo() {}
+};
+
+Foo* get_foo() {return new Foo();}
+%}
+
+%pythoncode %{
+    print_debug = True
+%}
+
+%extend Foo {
+    // Note that %pythoncode is not available with -builtin
+    %pythoncode %{
+    def __new__(cls, *args, **kwargs):
+        if print_debug:
+            print('in Foo.__new__()')
+        return super(Foo, cls).__new__(cls)
+
+    def __init__(self):
+        if print_debug:
+            print('in Foo.__init__()')
+    %}
+};