rather than passing locals to the class body, just execute the class body in the proper environment

Author: benjaminp

Doc/library/dis.rst

@@ -596,12 +596,6 @@ the stack so that it is available for further iterations of the loop.
    .. XXX explain the WHY stuff!
 
 
-.. opcode:: STORE_LOCALS
-
-   Pops TOS from the stack and stores it as the current frame's ``f_locals``.
-   This is used in class construction.
-
-
 All of the following opcodes expect arguments.  An argument is two bytes, with
 the more significant byte last.
 

Include/opcode.h

@@ -49,7 +49,6 @@ extern "C" {
 #define BINARY_OR       66
 #define INPLACE_POWER   67
 #define GET_ITER        68
-#define STORE_LOCALS    69
 #define PRINT_EXPR      70
 #define LOAD_BUILD_CLASS 71
 #define YIELD_FROM      72

Lib/importlib/_bootstrap.py

@@ -391,12 +391,13 @@ def _call_with_frames_removed(f, *args, **kwds):
 #     Python 3.4a1  3260 (add LOAD_CLASSDEREF; allow locals of class to override
 #                        free vars)
 #     Python 3.4a1  3270 (various tweaks to the __class_ closure)
+#     Python 3.4a1  3280 (remove implicit class argument)
 #
 # MAGIC must change whenever the bytecode emitted by the compiler may no
 # longer be understood by older implementations of the eval loop (usually
 # due to the addition of new opcodes).
 
-_MAGIC_BYTES = (3270).to_bytes(2, 'little') + b'\r\n'
+_MAGIC_BYTES = (3280).to_bytes(2, 'little') + b'\r\n'
 _RAW_MAGIC_NUMBER = int.from_bytes(_MAGIC_BYTES, 'little')
 
 _PYCACHE = '__pycache__'

Lib/opcode.py

@@ -84,7 +84,6 @@ def jabs_op(name, op):
 def_op('BINARY_OR', 66)
 def_op('INPLACE_POWER', 67)
 def_op('GET_ITER', 68)
-def_op('STORE_LOCALS', 69)
 
 def_op('PRINT_EXPR', 70)
 def_op('LOAD_BUILD_CLASS', 71)

Python/bltinmodule.c

@@ -57,6 +57,11 @@ builtin___build_class__(PyObject *self, PyObject *args, PyObject *kwds)
         return NULL;
     }
     func = PyTuple_GET_ITEM(args, 0); /* Better be callable */
+    if (!PyFunction_Check(func)) {
+        PyErr_SetString(PyExc_TypeError,
+                        "__build__class__: func must be a function");
+        return NULL;
+    }
     name = PyTuple_GET_ITEM(args, 1);
     if (!PyUnicode_Check(name)) {
         PyErr_SetString(PyExc_TypeError,
@@ -155,7 +160,9 @@ builtin___build_class__(PyObject *self, PyObject *args, PyObject *kwds)
         Py_DECREF(bases);
         return NULL;
     }
-    cell = PyObject_CallFunctionObjArgs(func, ns, NULL);
+    cell = PyEval_EvalCodeEx(PyFunction_GET_CODE(func), PyFunction_GET_GLOBALS(func), ns,
+                             NULL, 0, NULL, 0, NULL, 0, NULL,
+                             PyFunction_GET_CLOSURE(func));
     if (cell != NULL) {
         PyObject *margs;
         margs = PyTuple_Pack(3, name, bases, ns);

Python/ceval.c

@@ -1873,14 +1873,6 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
             goto error;
         }
 
-        TARGET(STORE_LOCALS) {
-            PyObject *locals = POP();
-            PyObject *old = f->f_locals;
-            Py_XDECREF(old);
-            f->f_locals = locals;
-            DISPATCH();
-        }
-
         TARGET(RETURN_VALUE) {
             retval = POP();
             why = WHY_RETURN;

Python/compile.c

@@ -893,8 +893,6 @@ opcode_stack_effect(int opcode, int oparg)
             return 7;
         case WITH_CLEANUP:
             return -1; /* XXX Sometimes more */
-        case STORE_LOCALS:
-            return -1;
         case RETURN_VALUE:
             return -1;
         case IMPORT_STAR:
@@ -1696,12 +1694,6 @@ compiler_class(struct compiler *c, stmt_ty s)
         Py_INCREF(s->v.ClassDef.name);
         Py_XDECREF(c->u->u_private);
         c->u->u_private = s->v.ClassDef.name;
-        /* force it to have one mandatory argument */
-        c->u->u_argcount = 1;
-        /* load the first argument (__locals__) ... */
-        ADDOP_I(c, LOAD_FAST, 0);
-        /* ... and store it into f_locals */
-        ADDOP_IN_SCOPE(c, STORE_LOCALS);
         /* load (global) __name__ ... */
         str = PyUnicode_InternFromString("__name__");
         if (!str || !compiler_nameop(c, str, Load)) {
@@ -4110,9 +4102,8 @@ compute_code_flags(struct compiler *c)
 {
     PySTEntryObject *ste = c->u->u_ste;
     int flags = 0, n;
-    if (ste->ste_type != ModuleBlock)
-        flags |= CO_NEWLOCALS;
     if (ste->ste_type == FunctionBlock) {
+        flags |= CO_NEWLOCALS;
         if (!ste->ste_unoptimized)
             flags |= CO_OPTIMIZED;
         if (ste->ste_nested)