Patch #1520294: Support for getset and member descriptors in types.py,

inspect.py, and pydoc.py.  Specifically, this allows for querying the type of
an object against these built-in C types and more importantly, for getting
their docstrings printed in the interactive interpreter's help() function.

This patch includes a new built-in module called _types which provides
definitions of getset and member descriptors for use by the types.py module.
These types are exposed as types.GetSetDescriptorType and
types.MemberDescriptorType.  Query functions are provided as
inspect.isgetsetdescriptor() and inspect.ismemberdescriptor().  The
implementations of these are robust enough to work with Python implementations
other than CPython, which may not have these fundamental types.

The patch also includes documentation and test suite updates.

I commit these changes now under these guiding principles:

1. Silence is assent.  The release manager has not said "no", and of the few
   people that cared enough to respond to the thread, the worst vote was "0".

2. It's easier to ask for forgiveness than permission.

3. It's so dang easy to revert stuff in svn, that you could view this as a
   forcing function. :)

Windows build patches will follow.

2 files changed, 98 insertions, 0 deletions

diff --git a/Modules/_typesmodule.c b/Modules/_typesmodule.c
new file mode 100644
index 0000000..5a6f2b9
--- /dev/null
+++ b/Modules/_typesmodule.c
@@ -0,0 +1,94 @@
+/* This extension module exposes some types that are only available at the
+ * C level.  It should not be used directly, but instead through the Python
+ * level types modules, which imports this.
+ */
+
+#include "Python.h"
+#include "structmember.h"
+
+typedef struct
+{
+    PyObject_HEAD
+    int member;
+} Helper;
+
+static PyMemberDef helper_members[] = {
+    { "member", T_INT,  offsetof(Helper, member), READONLY,
+      PyDoc_STR("A member descriptor")
+    },
+    { NULL }
+};
+
+static PyObject *
+helper_getter(Helper *self, void *unused) 
+{
+    Py_RETURN_NONE;
+}
+
+static PyGetSetDef helper_getset[] = {
+    { "getter", (getter)helper_getter, NULL,
+      PyDoc_STR("A getset descriptor"),
+    },
+    { NULL }
+};
+
+static PyTypeObject HelperType = {
+    PyObject_HEAD_INIT(NULL)
+    0,						/* ob_size */
+    "_types.Helper",				/* tp_name */
+    sizeof(Helper),                             /* tp_basicsize */
+    0,						/* tp_itemsize */
+    0,						/* tp_dealloc */
+    0,						/* tp_print */
+    0,						/* tp_getattr */
+    0,						/* tp_setattr */
+    0,						/* tp_compare */
+    0,                                          /* tp_repr */
+    0,                                          /* tp_as_number */
+    0,						/* tp_as_sequence */
+    0,						/* tp_as_mapping */
+    0,                                          /* tp_hash */
+    0,              				/* tp_call */
+    0,          				/* tp_str */
+    0,                                          /* tp_getattro */
+    0,						/* tp_setattro */
+    0,						/* tp_as_buffer */
+    Py_TPFLAGS_DEFAULT,                         /* tp_flags */
+    0,      					/* tp_doc */
+    0,						/* tp_traverse */
+    0,						/* tp_clear */
+    0,                                          /* tp_richcompare */
+    0,						/* tp_weaklistoffset */
+    0,						/* tp_iter */
+    0,						/* tp_iternext */
+    0,      					/* tp_methods */
+    helper_members,                             /* tp_members */
+    helper_getset,                              /* tp_getset */
+    0,						/* tp_base */
+    0,						/* tp_dict */
+    0,						/* tp_descr_get */
+    0,						/* tp_descr_set */
+    0,						/* tp_dictoffset */
+    0,						/* tp_init */
+    0,						/* tp_alloc */
+    0,                                          /* tp_new */
+    0,						/* tp_free */
+};
+
+PyMODINIT_FUNC
+init_types(void)
+{
+    PyObject *m;
+
+    m = Py_InitModule3("_types", NULL, "A types module helper");
+    if (!m)
+        return;
+
+    if (PyType_Ready(&HelperType) < 0)
+        return;
+
+    Py_INCREF(&HelperType);
+    PyModule_AddObject(m, "Helper", (PyObject *)&HelperType);
+}
+
+    
diff --git a/Modules/config.c.in b/Modules/config.c.in
index f811991..8c25eea 100644
--- a/Modules/config.c.in
+++ b/Modules/config.c.in
@@ -28,6 +28,7 @@ extern void PyMarshal_Init(void);
 extern void initimp(void);
 extern void initgc(void);
 extern void init_ast(void);
+extern void init_types(void);
 
 struct _inittab _PyImport_Inittab[] = {
 
@@ -42,6 +43,9 @@ struct _inittab _PyImport_Inittab[] = {
 	/* This lives in Python/Python-ast.c */
 	{"_ast", init_ast},
 
+	/* This lives in Python/_types.c */
+	{"_types", init_types},
+
 	/* These entries are here for sys.builtin_module_names */
 	{"__main__", NULL},
 	{"__builtin__", NULL},