Add warning for assignment to None, True and False. This is patch

549213 by Jeremy (checking in for him since he's away and busy).

Misc/NEWS

@@ -84,6 +84,10 @@ Type/class unification and new-style classes
 Core and builtins
 -----------------
 
+- Assignment to None has long been frowned upon.  Now there's a
+  warning message when you do this.  It also warns against assignment
+  to True or False.
+
 - A frame object's f_lineno attribute can now be written to from a
   trace function to change which line will execute next.  A command to
   exploit this from pdb has been added.  [SF patch #643835]

Python/compile.c

@@ -575,6 +575,7 @@ block_pop(struct compiling *c, int type)
 /* Prototype forward declarations */
 
 static int issue_warning(const char *, const char *, int);
+static int symtable_warn(struct symtable *, char *);
 static int com_init(struct compiling *, const char *);
 static void com_free(struct compiling *);
 static void com_push(struct compiling *, int);
@@ -1006,6 +1007,64 @@ none_assignment_check(struct compiling *c, char *name, int assigning)
 	return 0;
 }
 
+static int num_literals = 3;
+static char *literal_names[] = {"None", "True", "False"};
+static PyObject *literals;
+
+static int
+init_literals(void)
+{
+    int i;
+
+    literals = PyDict_New();
+    if (literals == NULL)
+	return -1;
+    for (i = 0; i < num_literals; i++)
+	if (PyDict_SetItemString(literals, literal_names[i], 
+				 Py_None) < 0) 
+	    return -1;
+    return 0;
+}
+
+static int
+check_literal(PyObject *name, struct compiling *c, struct symtable *st)
+{
+	/* check for literal names that will become keywords in the future */
+	if (literals == NULL && init_literals() < 0)
+		return -1;
+	if (!PyString_Check(name))
+		return -1;
+	if (PyDict_GetItem(literals, name)) {
+		char buf[1024];
+		PyOS_snprintf(buf, sizeof(buf), "'%s' may become a keyword", 
+			      PyString_AS_STRING(name));
+		if (c && (issue_warning(buf, c->c_filename, c->c_lineno) < 0))
+			return -1;
+		if (st && (symtable_warn(st, buf) < 0))
+			return -1;
+	}
+	return 0;
+}
+
+static int
+check_literal_str(const char *name, struct compiling *c, struct symtable *st)
+{
+	int i;
+
+	for (i = 0; i < num_literals; i++)
+		if (strcmp(literal_names[i], name) == 0) {
+			char buf[1024];
+			PyOS_snprintf(buf, sizeof(buf), 
+				      "'%s' may become a keyword", name);
+			if (c && 
+			    issue_warning(buf, c->c_filename, c->c_lineno) < 0)
+				return -1;
+			if (st && symtable_warn(st, buf) < 0)
+				return -1;
+		}
+	return 0;
+}
+
 static void
 com_addop_varname(struct compiling *c, int kind, char *name)
 {
@@ -1063,6 +1122,14 @@ com_addop_varname(struct compiling *c, int kind, char *name)
 	}
 	Py_DECREF(v);
 
+	if (kind == VAR_STORE || kind == VAR_DELETE) {
+		if (check_literal(v, c, NULL) < 0) {
+			c->c_errors++;
+			i = 255;
+			goto done;
+		}
+	}
+
 	switch (kind) {
 	case VAR_LOAD:
 		switch (scope) {
@@ -1130,6 +1197,7 @@ com_addopname(struct compiling *c, int op, node *n)
 	/* XXX it is possible to write this code without the 1000
 	   chars on the total length of dotted names, I just can't be
 	   bothered right now */
+
 	if (TYPE(n) == STAR)
 		name = "*";
 	else if (TYPE(n) == dotted_name) {
@@ -1138,6 +1206,10 @@ com_addopname(struct compiling *c, int op, node *n)
 		name = buffer;
 		for (i = 0; i < NCH(n); i += 2) {
 			char *s = STR(CHILD(n, i));
+			if (check_literal_str(s, c, NULL) < 0) {
+			    name = NULL;
+			    break;
+			}
 			if (p + strlen(s) > buffer + (sizeof buffer) - 2) {
 				com_error(c, PyExc_MemoryError,
 					  "dotted_name too long");
@@ -1153,6 +1225,8 @@ com_addopname(struct compiling *c, int op, node *n)
 	else {
 		REQ(n, NAME);
 		name = STR(n);
+		if (check_literal_str(name, c, NULL) < 0)
+		    name = NULL;
 	}
 	com_addop_name(c, op, name);
 }
@@ -2972,9 +3046,13 @@ com_import_stmt(struct compiling *c, node *n)
 		} else {
 			tup = PyTuple_New((NCH(n) - 2)/2);
 			for (i = 3; i < NCH(n); i += 2) {
+				char *s = STR(CHILD(CHILD(n, i), 0));
+				if (check_literal_str(s, c, NULL) < 0) {
+					c->c_errors++;
+					return;
+				}
 				PyTuple_SET_ITEM(tup, (i-3)/2, 
-					PyString_FromString(STR(
-						CHILD(CHILD(n, i), 0))));
+						 PyString_FromString(s));
 			}
 		}
 		com_addoparg(c, LOAD_CONST, com_addconst(c, tup));
@@ -3914,40 +3992,23 @@ com_fplist(struct compiling *c, node *n)
 static void
 com_arglist(struct compiling *c, node *n)
 {
-	int nch, i, narg;
+	int i;
 	int complex = 0;
-	char nbuf[30];
 	REQ(n, varargslist);
 	/* varargslist:
 		(fpdef ['=' test] ',')* (fpdef ['=' test] | '*' .....) */
-	nch = NCH(n);
-	/* Enter all arguments in table of locals */
-	for (i = 0, narg = 0; i < nch; i++) {
-		node *ch = CHILD(n, i);
-		node *fp;
-		if (TYPE(ch) == STAR || TYPE(ch) == DOUBLESTAR)
-			break;
-		REQ(ch, fpdef); /* fpdef: NAME | '(' fplist ')' */
-		fp = CHILD(ch, 0);
-		if (TYPE(fp) != NAME) {
-			PyOS_snprintf(nbuf, sizeof(nbuf), ".%d", i);
+	/* Check if the argument list includes nested tuples */
+	for (i = 0; i < NCH(n); i++)
+		if (TYPE(CHILD(n, i)) == LPAR) {
 			complex = 1;
-		}
-		narg++;
-		/* all name updates handled by symtable */
-		if (++i >= nch)
 			break;
-		ch = CHILD(n, i);
-		if (TYPE(ch) == EQUAL)
-			i += 2;
-		else
-			REQ(ch, COMMA);
-	}
+		}
+	/* If it does, generate code to unpack them. */
 	if (complex) {
 		/* Generate code for complex arguments only after
 		   having counted the simple arguments */
 		int ilocal = 0;
-		for (i = 0; i < nch; i++) {
+		for (i = 0; i < NCH(n); i++) {
 			node *ch = CHILD(n, i);
 			node *fp;
 			if (TYPE(ch) == STAR || TYPE(ch) == DOUBLESTAR)
@@ -3960,7 +4021,7 @@ com_arglist(struct compiling *c, node *n)
 				com_fpdef(c, ch);
 			}
 			ilocal++;
-			if (++i >= nch)
+			if (++i >= NCH(n))
 				break;
 			ch = CHILD(n, i);
 			if (TYPE(ch) == EQUAL)
@@ -5359,7 +5420,7 @@ static void
 symtable_params(struct symtable *st, node *n)
 {
 	int i, complex = -1, ext = 0;
-	node *c = NULL;
+	node *c = NULL, *ch = NULL;
 
 	if (TYPE(n) == parameters) {
 		n = CHILD(n, 1);
@@ -5376,9 +5437,14 @@ symtable_params(struct symtable *st, node *n)
 		if (TYPE(c) == test) {
 			continue;
 		}
-		if (TYPE(CHILD(c, 0)) == NAME)
+		ch = CHILD(c, 0);
+		if (TYPE(ch) == NAME) {
+			if (check_literal_str(STR(ch), NULL, st) < 0) {
+				st->st_errors++;
+				return;
+			}
 			symtable_add_def(st, STR(CHILD(c, 0)), DEF_PARAM);
-		else {
+		} else {
 			char nbuf[30];
 			PyOS_snprintf(nbuf, sizeof(nbuf), ".%d", i);
 			symtable_add_def(st, nbuf, DEF_PARAM);