Fix constantification of None.

Lib/test/test_peepholer.py

@@ -49,6 +49,11 @@ class TestTranforms(unittest.TestCase):
             self.assert_(elem not in asm)
         for elem in ('LOAD_CONST', '(None)'):
             self.assert_(elem in asm)
+        def f():
+            'Adding a docstring made this test fail in Py2.5.0'
+            return None
+        self.assert_('LOAD_CONST' in disassemble(f))
+        self.assert_('LOAD_GLOBAL' not in disassemble(f))
 
     def test_while_one(self):
         # Skip over:  LOAD_CONST trueconst  JUMP_IF_FALSE xx  POP_TOP

Misc/NEWS

@@ -15,6 +15,9 @@ Core and builtins
 - Bug #1669182: prevent crash when trying to print an unraisable error
   from a string exception.
 
+- The peephole optimizer left None as a global in functions with a docstring
+  and an explicit return value.
+
 - Bug #1653736: Properly discard third argument to slot_nb_inplace_power.
 
 - SF #151204:  enumerate() now raises an Overflow error at sys.maxint items.

Python/compile.c

@@ -773,13 +773,17 @@ optimize_code(PyObject *code, PyObject* consts, PyObject *names,
 				if (name == NULL  ||  strcmp(name, "None") != 0)
 					continue;
 				for (j=0 ; j < PyList_GET_SIZE(consts) ; j++) {
-					if (PyList_GET_ITEM(consts, j) == Py_None) {
-						codestr[i] = LOAD_CONST;
-						SETARG(codestr, i, j);
-						cumlc = lastlc + 1;
+					if (PyList_GET_ITEM(consts, j) == Py_None)
 						break;
-					}
 				}
+				if (j == PyList_GET_SIZE(consts)) {
+					if (PyList_Append(consts, Py_None) == -1)
+					        goto exitUnchanged;                                        
+				}
+				assert(PyList_GET_ITEM(consts, j) == Py_None);
+				codestr[i] = LOAD_CONST;
+				SETARG(codestr, i, j);
+				cumlc = lastlc + 1;
 				break;
 
 				/* Skip over LOAD_CONST trueconst