diff -r 3a069e5593ef Python/bltinmodule.c
--- a/Python/bltinmodule.c	Wed May 04 23:26:04 2016 +0300
+++ b/Python/bltinmodule.c	Fri May 06 10:03:43 2016 -0500
@@ -1310,6 +1310,115 @@
 is exhausted, it is returned instead of raising StopIteration.");
 
 
+/* AC: cannot convert yet, as needs arbitrary keyword arguments. */
+static PyObject *
+builtin_public(PyObject *self, PyObject *args, PyObject *kwds)
+{
+    PyObject *arg = NULL;
+    PyObject *globals = NULL;
+    PyObject *all = NULL;
+
+    if (!PyArg_UnpackTuple(args, "public", 0, 1, &arg))
+        return NULL;
+
+    /* kwds can be empty, but the keys must be strings. */
+    if (kwds != NULL && !PyArg_ValidateKeywordArguments(kwds))
+        return NULL;
+
+    if (kwds != NULL && !PyDict_Check(kwds)) {
+        PyErr_BadInternalCall();
+        return NULL;
+    }
+    if (!(globals = PyEval_GetGlobals())) {
+        PyErr_Format(PyExc_TypeError,
+                     "@public called with no active globals");
+        return NULL;
+    }
+    if (!(all = PyDict_GetItemString(globals, "__all__"))) {
+        if (!(all = PyList_New(0)))
+            return NULL;
+        if (PyDict_SetItemString(globals, "__all__", all) < 0)
+            goto err;
+    }
+    else
+        /* Bump all's reference count since it's currently borrowed, and this
+           way we guarantee we own a reference for common exit cleanup.
+        */
+        Py_INCREF(all);
+
+    if (arg != NULL) {
+        PyObject *name = NULL;
+
+        /* There is a single positional argument.  This must have a "__name__"
+           attribute, which we will put in __all__.  The keywords dictionary
+           must be empty.
+        */
+        if (kwds != NULL && PyDict_Size(kwds) != 0) {
+            PyErr_Format(PyExc_TypeError,
+                         "Positional and keywords are mutually exclusive");
+            goto err;
+        }
+        if (!PyObject_HasAttrString(arg, "__name__")) {
+            PyErr_Format(PyExc_TypeError,
+                         "Positional argument has no __name__");
+            goto err;
+        }
+        if (!(name = PyObject_GetAttrString(arg, "__name__")) ||
+            !PyUnicode_Check(name))
+        {
+            Py_XDECREF(name);
+            goto err;
+        }
+        if (PyList_Append(all, name) < 0) {
+            Py_XDECREF(name);
+            goto err;
+        }
+    }
+    else if (kwds == NULL || PyDict_Size(kwds) == 0) {
+        PyErr_Format(
+            PyExc_TypeError,
+            "Either a single positional or keyword arguments required");
+        goto err;
+    }
+    else {
+        /* There are only keyword arguments, so for each of these, insert the
+           key in __all__ *and* bind the name/key to the value in globals.  We
+           force the use of globals here because we're modifying the global
+           __all__ so it doesn't make sense to touch locals.
+        */
+        PyObject *key, *value;
+        Py_ssize_t pos = 0;
+
+        while (PyDict_Next(kwds, &pos, &key, &value)) {
+            if (PyList_Append(all, key) < 0)
+                goto err;
+            if (PyDict_SetItem(globals, key, value) < 0)
+                goto err;
+        }
+    }
+
+    Py_XDECREF(all);
+    Py_RETURN_NONE;
+
+  err:
+    Py_XDECREF(all);
+    return NULL;
+}
+
+PyDoc_STRVAR(public_doc,
+"public(named, **kws)\n\
+\n\
+May be used as a decorator or called directly.  When used as a decorator\n\
+the thing being decorated must have an __name__ attribute.  The value of\n\
+__name__ will be inserted in the global __all__ list.  In this use case\n\
+it is an error to also include keyword arguments.\n\
+\n\
+When called directly, it is an error to pass a positional argument.  The\n\
+keys must be strings, and are inserted into the global __all__ list. The\n\
+mapping of keys to values is also inserted into the globals, thus creating\n\
+name bindings for each key/value pair.");
+
+
 /*[clinic input]
 setattr as builtin_setattr
 
@@ -2618,6 +2727,7 @@
     BUILTIN_ORD_METHODDEF
     BUILTIN_POW_METHODDEF
     {"print",           (PyCFunction)builtin_print,      METH_VARARGS | METH_KEYWORDS, print_doc},
+    {"public",          (PyCFunction)builtin_public,     METH_VARARGS | METH_KEYWORDS, public_doc},
     BUILTIN_REPR_METHODDEF
     {"round",           (PyCFunction)builtin_round,      METH_VARARGS | METH_KEYWORDS, round_doc},
     BUILTIN_SETATTR_METHODDEF