Add example to test the Python module being renamed to __init__.py

This examples tests the SWIG generated module being placed into a directory and
then renamed __init__.py to convert the module into a package. This ability
stopped working in swig-3.0.9. However, only Python 2.7 or 3.3 and later work. If
Python 3.2 support is needed, use moduleimport in %module to customise the import
code.

Issue #1282

Examples/python/import_packages/Makefile

@@ -8,6 +8,7 @@ import_packages_subdirs = \
 	from_init1 \
 	from_init2 \
 	from_init3 \
+	module_is_init \
 	relativeimport1 \
 	relativeimport2 \
 	relativeimport3 \

Examples/python/import_packages/module_is_init/Makefile

@@ -0,0 +1,15 @@
+TOP        = ../../..
+LIBS       =
+
+check: build
+	$(MAKE) -f $(TOP)/Makefile SRCDIR='$(SRCDIR)' python_run
+
+build:
+	cd pkg1 && $(MAKE) SWIGOPT='$(SWIGOPT)' LIBS='$(LIBS)' build
+
+static:
+	cd pkg1 && $(MAKE) SWIGOPT='$(SWIGOPT)' LIBS='$(LIBS)' static
+
+clean:
+	$(MAKE) -f $(TOP)/Makefile SRCDIR='$(SRCDIR)' python_clean
+	cd pkg1 && $(MAKE) clean

Examples/python/import_packages/module_is_init/README

@@ -0,0 +1,18 @@
+This example tests renaming the generated SWIG pure Python module to __init__.py
+to turn the module into a Python package.
+
+Use 'python runme.py' to run the test.
+
+Overview:
+---------
+
+SWIG generates a pure Python module foo.py from the input interface file foo.i.
+The foo.py file is generated within the pkg1 directory and is then renamed __init__.py.
+This results in everything in the SWIG generated module being available in the Python
+pkg1 package.
+
+This approach of turning the SWIG generated module into a package worked in versions
+of SWIG up to swig-3.0.8, but stopped working from swig-3.0.9 until it was
+re-instated in swig-4.0.0. However, Python 2.7 or 3.3 and later are needed to
+work out of the box. Python 3.2 does not work as this version of Python does
+not set __package__ in __init__.py.

Examples/python/import_packages/module_is_init/pkg1/Makefile

@@ -0,0 +1,20 @@
+TOP        = ../../../..
+SWIGEXE    = $(TOP)/../swig
+SWIG_LIB_DIR = $(TOP)/../$(TOP_BUILDDIR_TO_TOP_SRCDIR)Lib
+SWIGOPT    =
+LIBS       =
+
+build:
+	$(MAKE) -f $(TOP)/Makefile SRCDIR='$(SRCDIR)' \
+	SWIG_LIB_DIR='$(SWIG_LIB_DIR)' SWIGEXE='$(SWIGEXE)' \
+	SWIGOPT='$(SWIGOPT)' LIBS='$(LIBS)' TARGET='foo' INTERFACE='foo.i' python_cpp
+	mv foo.py __init__.py
+
+static:
+	$(MAKE) -f $(TOP)/Makefile SRCDIR='$(SRCDIR)' \
+	SWIG_LIB_DIR='$(SWIG_LIB_DIR)' SWIGEXE='$(SWIGEXE)' \
+	SWIGOPT='$(SWIGOPT)' LIBS='$(LIBS)' TARGET='foo' INTERFACE='foo.i' python_cpp_static
+
+clean:
+	$(MAKE) -f $(TOP)/Makefile SRCDIR='$(SRCDIR)' TARGET='foo' python_clean
+	rm -f __init__.py

Examples/python/import_packages/module_is_init/pkg1/foo.hpp

@@ -0,0 +1,10 @@
+
+int foofunction(int i) {
+  return i *= 10;
+}
+
+struct FooClass {
+  int foomethod(int i) {
+    return i += 5;
+  }
+};

Examples/python/import_packages/module_is_init/pkg1/foo.i

@@ -0,0 +1,5 @@
+%module foo
+%{
+#include "./foo.hpp"
+%}
+%include "./foo.hpp"

Examples/python/import_packages/module_is_init/runme.py

@@ -0,0 +1,26 @@
+import os.path
+import sys
+
+# Test import of a SWIG generated module renamed as the package's __init__.py
+testname = os.path.basename(os.path.dirname(os.path.abspath(__file__)))
+print "Testing " + testname + " - module renamed as __init__.py"
+
+if sys.version_info >= (3, 0, 0) and sys.version_info < (3, 3, 0):
+    print "  Not importing as Python version is >= 3.0 and < 3.3"
+    # Package detection does not work in these versions.
+    # Can be fixed by using this in the interface file:
+    #   %module(moduleimport="from . import $module") foo   # without -builtin
+    #   %module(moduleimport="from .$module import *") foo  # with -builtin
+    sys.exit(0)
+
+import pkg1
+print "  Finished importing pkg1"
+
+if pkg1.foofunction(123) != 1230:
+    raise RuntimeError("foofunction failed")
+
+fc = pkg1.FooClass()
+if fc.foomethod(1) != 6:
+    raise RuntimeError("foomethod failed")
+
+print "  Finished testing pkg1"