Add CYTHON_NO_PYINIT_EXPORT macro. (#1944)

When building the generated code in an embedded interpreter the module
init function will no longer be exported if CYTHON_NO_PYINIT_EXPORT is defined.

See https://github.com/cython/cython/issues/1944 for details.

Cython/Compiler/ModuleNode.py

@@ -2261,8 +2261,28 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
     def generate_module_init_func(self, imported_modules, env, code):
         code.enter_cfunc_scope(self.scope)
         code.putln("")
-        header2 = "PyMODINIT_FUNC init%s(void)" % env.module_name
-        header3 = "PyMODINIT_FUNC %s(void)" % self.mod_init_func_cname('PyInit', env)
+        code.putln("#if PY_MAJOR_VERSION < 3")
+        code.putln("#ifdef CYTHON_NO_PYINIT_EXPORT")
+        code.putln("/* define this to void manually because PyMODINIT_FUNC")
+        code.putln("* adds __declspec(dllexport) to it's definition.")
+        code.putln("*/")
+        code.putln("#define __Pyx_PyMODINIT_FUNC void")
+        code.putln("#else")
+        code.putln("#define __Pyx_PyMODINIT_FUNC PyMODINIT_FUNC")
+        code.putln("#endif")
+        code.putln("#else")
+        code.putln("#ifdef CYTHON_NO_PYINIT_EXPORT")
+        code.putln("/* define this to PyObject * manually because PyMODINIT_FUNC")
+        code.putln("* adds __declspec(dllexport) to it's definition.")
+        code.putln("*/")
+        code.putln("#define __Pyx_PyMODINIT_FUNC PyObject *")
+        code.putln("#else")
+        code.putln("#define __Pyx_PyMODINIT_FUNC PyMODINIT_FUNC")
+        code.putln("#endif")
+        code.putln("#endif")
+        code.putln("")
+        header2 = "__Pyx_PyMODINIT_FUNC init%s(void)" % env.module_name
+        header3 = "__Pyx_PyMODINIT_FUNC %s(void)" % self.mod_init_func_cname('PyInit', env)
         code.putln("#if PY_MAJOR_VERSION < 3")
         code.putln("%s; /*proto*/" % header2)
         code.putln(header2)

docs/src/reference/compilation.rst

@@ -43,6 +43,44 @@ paths to libraries you need to link with]
 A ``yourmod.so`` file is now in the same directory and your module,
 ``yourmod``, is available for you to import as you normally would.
 
+Compiling in a embedded interpreter
+===================================
+
+Sometimes you might want to use cython to compile a python module you
+made into your hand made embedded python. Here is how to do that.
+
+On the top of your C file above the main function you created
+type this without the quotes::
+
+    PyMODINIT_FUNC PyInit__test(void);
+
+for python 3.x and::
+
+    PyMODINIT_FUNC init_test(void);
+
+for python 2.
+
+Where Module Name is the name of the module you cythonized. If you
+are not sure on the name of the module init function refer to your
+generated module source file.
+
+You need to use ``PyImport_AppendInittab`` but right
+before you use ``Py_SetProgramName`` and ``Py_Initialize`` in your
+main as well::
+
+    PyImport_AppendInittab("_test", PyInit__test);
+
+for python 3.x and::
+
+    PyImport_AppendInittab("_test", init_test)
+
+After that is done go in and for all the sources you use define the
+following in the compiler's command line::
+
+    CYTHON_NO_PYINIT_EXPORT
+
+This macro is to ensure that your module initialization function is
+not exported.
 
 Compiling with ``distutils``
 ============================