complain about "global __class__" in a class body (closes #17983)

Author: benjaminp

Lib/test/test_scope.py

@@ -743,6 +743,10 @@ def dig(self):
         del tester
         self.assertIsNone(ref())
 
+    def test__Class__Global(self):
+        s = "class X:\n    global __class__\n    def f(self): super()"
+        self.assertRaises(SyntaxError, exec, s)
+
 
 def test_main():
     run_unittest(ScopeTests)

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 3.3.3 release candidate 1?
 Core and Builtins
 -----------------
 
+- Issue #17983: Raise a SyntaxError for a ``global __class__`` statement in a
+  class body.
+
 - Issue #17927: Frame objects kept arguments alive if they had been copied into
   a cell, even if the cell was cleared.
 

Python/symtable.c

@@ -1236,6 +1236,12 @@ symtable_visit_stmt(struct symtable *st, stmt_ty s)
         asdl_seq *seq = s->v.Global.names;
         for (i = 0; i < asdl_seq_LEN(seq); i++) {
             identifier name = (identifier)asdl_seq_GET(seq, i);
+            if (st->st_cur->ste_type == ClassBlock &&
+                !PyUnicode_CompareWithASCIIString(name, "__class__")) {
+                PyErr_SetString(PyExc_SyntaxError, "cannot make __class__ global");
+                PyErr_SyntaxLocationEx(st->st_filename, s->lineno, s->col_offset);
+                return 0;
+            }
             long cur = symtable_lookup(st, name);
             if (cur < 0)
                 VISIT_QUIT(st, 0);