Add warning for 5 features.

Include/ceval.h

@@ -30,6 +30,7 @@ PyAPI_FUNC(PyObject *) PyEval_GetGlobals(void);
 PyAPI_FUNC(PyObject *) PyEval_GetLocals(void);
 PyAPI_FUNC(struct _frame *) PyEval_GetFrame(void);
 PyAPI_FUNC(int) PyEval_GetRestricted(void);
+PyAPI_FUNC(int) _Py3kWarn_NextOpcode(void);
 
 /* Look at the current frame's (if any) code's co_flags, and turn on
    the corresponding compiler flags in cf->cf_flags.  Return 1 if any

Lib/contextlib.py

@@ -14,14 +14,14 @@ def __init__(self, gen):
 
     def __enter__(self):
         try:
-            return self.gen.next()
+            return next(self.gen)
         except StopIteration:
             raise RuntimeError("generator didn't yield")
 
     def __exit__(self, type, value, traceback):
         if type is None:
             try:
-                self.gen.next()
+                next(self.gen)
             except StopIteration:
                 return
             else:

Lib/test/test_py3kwarn.py

@@ -221,6 +221,34 @@ def test_sort_cmp_arg(self):
             w.reset()
             self.assertWarning(sorted(lst, cmp), w, expected)
 
+    def test_next_method(self):
+        expected = 'iterator.next() is not supported in 3.x; use __next__() instead'
+        it = iter(range(5))
+        with check_py3k_warnings() as w:
+            self.assertWarning(it.next(), w, expected)
+
+    def test_intern(self):
+        expected = 'intern() is not supported in 3.x: use sys.intern() instead'
+        with check_py3k_warnings() as w:
+            self.assertWarning(intern('pygrate-next-method'), w, expected)
+
+    def test_range_materialization(self):
+        expected = 'range() may require list materialization in 3.x'
+        with check_py3k_warnings() as w:
+            self.assertWarning(range(5) + [5], w, expected)
+
+    def test_xrange_materialization(self):
+        expected = 'xrange() may require list materialization in 3.x'
+        with check_py3k_warnings() as w:
+            items = xrange(5)
+            self.assertWarning(None, w, expected)
+
+    def test_dict_listlike_materialization(self):
+        expected = 'dict.keys() may require list materialization in 3.x'
+        d = {'a': 1, 'b': 2}
+        with check_py3k_warnings() as w:
+            self.assertWarning(d.keys()[0], w, expected)
+
     def test_sys_exc_clear(self):
         expected = 'sys.exc_clear() not supported in 3.x; use except clauses'
         with check_py3k_warnings() as w:
@@ -288,9 +316,10 @@ def test_bytesio_truncate(self):
         from io import BytesIO
         x = BytesIO(b'AAAAAA')
         expected = "BytesIO.truncate() does not shift the file pointer: use seek(0) before doing truncate(0)"
-        self.assertWarning(x.truncate(0), w, expected)
-        w.reset()
-        self.assertNoWarning(x.truncate(-1), w)
+        with check_py3k_warnings() as w:
+            self.assertWarning(x.truncate(0), w, expected)
+            w.reset()
+            self.assertNoWarning(x.truncate(-1), w)
 
     def test_file_open(self):
         expected = ("The builtin 'file()'/'open()' function is not supported in 3.x, "

Objects/dictobject.c

@@ -8,6 +8,7 @@
 */
 
 #include "Python.h"
+#include "opcode.h"
 
 
 /* Set a key error with the specified argument, wrapping it in a
@@ -27,6 +28,15 @@ set_key_error(PyObject *arg)
 /* Define this out if you don't want conversion statistics on exit. */
 #undef SHOW_CONVERSION_COUNTS
 
+#define WARN_DICT_LISTLIKE(MSG) \
+    do { \
+        int nextop = _Py3kWarn_NextOpcode(); \
+        if ((nextop == BINARY_SUBSCR || nextop == STORE_SUBSCR || \
+                nextop == BINARY_ADD || nextop == INPLACE_ADD) && \
+                PyErr_WarnPy3k((MSG), 1) < 0) \
+            return NULL; \
+    } while (0)
+
 /* See large comment block below.  This must be >= 1. */
 #define PERTURB_SHIFT 5
 
@@ -1301,6 +1311,8 @@ dict_keys(register PyDictObject *mp)
     PyDictEntry *ep;
     Py_ssize_t mask, n;
 
+    WARN_DICT_LISTLIKE("dict.keys() may require list materialization in 3.x");
+
   again:
     n = mp->ma_used;
     v = PyList_New(n);
@@ -1335,6 +1347,8 @@ dict_values(register PyDictObject *mp)
     PyDictEntry *ep;
     Py_ssize_t mask, n;
 
+    WARN_DICT_LISTLIKE("dict.values() may require list materialization in 3.x");
+
   again:
     n = mp->ma_used;
     v = PyList_New(n);
@@ -1370,6 +1384,8 @@ dict_items(register PyDictObject *mp)
     PyObject *item, *key, *value;
     PyDictEntry *ep;
 
+    WARN_DICT_LISTLIKE("dict.items() may require list materialization in 3.x");
+
     /* Preallocate the list of tuples, to avoid allocations during
      * the loop over the items, which could trigger GC, which
      * could resize the dict. :-(

Objects/rangeobject.c

@@ -1,6 +1,7 @@
 /* Range object implementation */
 
 #include "Python.h"
+#include "opcode.h"
 
 typedef struct {
     PyObject_HEAD
@@ -67,8 +68,15 @@ range_new(PyTypeObject *type, PyObject *args, PyObject *kw)
     rangeobject *obj;
     long ilow = 0, ihigh = 0, istep = 1;
     unsigned long n;
+    int nextop;
 
-    if (PyErr_WarnPy3k_WithFix("xrange() is not supported in 3.x", "use range() instead", 1) < 0)
+    nextop = _Py3kWarn_NextOpcode();
+    if (nextop == GET_ITER &&
+            PyErr_WarnPy3k_WithFix("xrange() is not supported in 3.x",
+                                   "use range() instead", 1) < 0)
+        return NULL;
+    if (nextop != GET_ITER &&
+            PyErr_WarnPy3k("xrange() may require list materialization in 3.x", 1) < 0)
         return NULL;
 
     if (!_PyArg_NoKeywords("xrange()", kw))

Objects/typeobject.c

@@ -4857,6 +4857,10 @@ wrap_next(PyObject *self, PyObject *args, void *wrapped)
 
     if (!check_num_args(args, 0))
         return NULL;
+    if (Py_TYPE(self)->tp_iter != NULL &&
+            PyErr_WarnPy3k("iterator.next() is not supported in 3.x; "
+                           "use __next__() instead", 1) < 0)
+        return NULL;
     res = (*func)(self);
     if (res == NULL && !PyErr_Occurred())
         PyErr_SetNone(PyExc_StopIteration);

Python/bltinmodule.c

@@ -6,6 +6,7 @@
 #include "node.h"
 #include "code.h"
 #include "eval.h"
+#include "opcode.h"
 
 #include <ctype.h>
 #include <float.h> /* for DBL_MANT_DIG and friends */
@@ -1282,6 +1283,9 @@ builtin_intern(PyObject *self, PyObject *args)
                         "can't intern subclass of string");
         return NULL;
     }
+    if (PyErr_WarnPy3k("intern() is not supported in 3.x: use sys.intern() instead",
+                       1) < 0)
+        return NULL;
     Py_INCREF(s);
     PyString_InternInPlace(&s);
     return s;
@@ -1970,9 +1974,15 @@ builtin_range(PyObject *self, PyObject *args)
     long ilow = 0, ihigh = 0, istep = 1;
     long bign;
     Py_ssize_t i, n;
+    int nextop;
 
     PyObject *v;
 
+    nextop = _Py3kWarn_NextOpcode();
+    if ((nextop == BINARY_ADD || nextop == INPLACE_ADD) &&
+            PyErr_WarnPy3k("range() may require list materialization in 3.x", 1) < 0)
+        return NULL;
+
     if (PyTuple_Size(args) <= 1) {
         if (!PyArg_ParseTuple(args,
                         "l;range() requires 1-3 int arguments",

Python/ceval.c

@@ -19,6 +19,53 @@
 
 #include <ctype.h>
 
+int
+_Py3kWarn_NextOpcode(void)
+{
+    PyFrameObject *frame;
+    char *code;
+    Py_ssize_t n;
+    int offset;
+    int op;
+    int steps;
+
+    frame = PyEval_GetFrame();
+    if (frame == NULL || frame->f_code == NULL)
+        return -1;
+    if (PyString_AsStringAndSize(frame->f_code->co_code, &code, &n) < 0) {
+        PyErr_Clear();
+        return -1;
+    }
+
+    offset = frame->f_lasti;
+    if (offset < 0 || offset >= n)
+        return -1;
+
+    op = (unsigned char)code[offset];
+    offset += 1;
+    if (HAS_ARG(op))
+        offset += 2;
+
+    /* These warnings only care about the immediate consumer of the
+       just-evaluated call result. Looking ahead a handful of opcodes is
+       enough to skip trivial stack setup before we either find a relevant
+       consumer or hit a stop opcode showing the value has already been
+       stored, returned, or discarded. */
+    for (steps = 0; steps < 8 && offset >= 0 && offset < n; steps++) {
+        op = (unsigned char)code[offset];
+        if (op == BINARY_ADD || op == INPLACE_ADD || op == GET_ITER ||
+                op == BINARY_SUBSCR || op == STORE_SUBSCR)
+            return op;
+        if (op == RETURN_VALUE || op == STORE_NAME || op == STORE_FAST ||
+                op == STORE_GLOBAL || op == STORE_ATTR || op == POP_TOP)
+            return -1;
+        offset += 1;
+        if (HAS_ARG(op))
+            offset += 2;
+    }
+    return -1;
+}
+
 #ifndef WITH_TSC
 
 #define READ_TIMESTAMP(var)