def test():
  globals()['a2'] = 4
test()
print a2  # 输出 4

def aaaa():
  print locals()
  for i in ['a', 'b', 'c']:
    locals()[i] = 1
  print locals()
  print a
aaaa()

def aaaa():
  print locals()
  s = 'test'          # 加入显示赋值 s    
  for i in ['a', 'b', 'c']:
    locals()[i] = 1
  print locals()
  print s            # 打印局部变量 s 
  print a
aaaa()

13      0 LOAD_GLOBAL       0 (locals)
       3 CALL_FUNCTION      0
       6 PRINT_ITEM
       7 PRINT_NEWLINE

 14      8 LOAD_CONST        1 ('test')
       11 STORE_FAST        0 (s)

 15     14 SETUP_LOOP       36 (to 53)
       17 LOAD_CONST        2 ('a')
       20 LOAD_CONST        3 ('b')
       23 LOAD_CONST        4 ('c')
       26 BUILD_LIST        3
       29 GET_ITER
      30 FOR_ITER        19 (to 52)
       33 STORE_FAST        1 (i)

 16     36 LOAD_CONST        5 (1)
       39 LOAD_GLOBAL       0 (locals)
       42 CALL_FUNCTION      0
       45 LOAD_FAST        1 (i)
       48 STORE_SUBSCR
       49 JUMP_ABSOLUTE      30
      52 POP_BLOCK

 17     53 LOAD_GLOBAL       0 (locals)
       56 CALL_FUNCTION      0
       59 PRINT_ITEM
       60 PRINT_NEWLINE

 18     61 LOAD_FAST        0 (s)
       64 PRINT_ITEM
       65 PRINT_NEWLINE

 19     66 LOAD_GLOBAL       1 (a)
       69 PRINT_ITEM
       70 PRINT_NEWLINE
       71 LOAD_CONST        0 (None)
       74 RETURN_VALUE
None

// ceval.c 从上往下, 依次是相应函数或者变量的定义
// 指令源码
TARGET(STORE_FAST)
{
  v = POP();
  SETLOCAL(oparg, v);
  FAST_DISPATCH();
}
--------------------
// SETLOCAL 宏定义   
#define SETLOCAL(i, value)   do { PyObject *tmp = GETLOCAL(i);                    GETLOCAL(i) = value;                    Py_XDECREF(tmp); } while (0)
-------------------- 
// GETLOCAL 宏定义                  
#define GETLOCAL(i)   (fastlocals[i])   

-------------------- 
// fastlocals 真面目
PyObject * PyEval_EvalFrameEx(PyFrameObject *f, int throwflag){
  // 省略其他无关代码
  fastlocals = f->f_localsplus;
....
}

// bltinmodule.c
static PyMethodDef builtin_methods[] = {
  ...
  // 找到 locals 函数对应的内置函数是 builtin_locals 
  {"locals",     (PyCFunction)builtin_locals,   METH_NOARGS, locals_doc},
  ...
}

-----------------------------

// builtin_locals 的定义
static PyObject *
builtin_locals(PyObject *self)
{
  PyObject *d;

  d = PyEval_GetLocals();
  Py_XINCREF(d);
  return d;
}
-----------------------------

PyObject *
PyEval_GetLocals(void)
{
  PyFrameObject *current_frame = PyEval_GetFrame(); // 获取当前堆栈对象
  if (current_frame == NULL)
    return NULL;
  PyFrame_FastToLocals(current_frame); // 初始化和填充 f_locals
  return current_frame->f_locals;
}
-----------------------------

// 初始化和填充 f_locals 的具体实现
void
PyFrame_FastToLocals(PyFrameObject *f)
{
  /* Merge fast locals into f->f_locals */
  PyObject *locals, *map;
  PyObject **fast;
  PyObject *error_type, *error_value, *error_traceback;
  PyCodeObject *co;
  Py_ssize_t j;
  int ncells, nfreevars;
  if (f == NULL)
    return;
  locals = f->f_locals;
  
  // 如果locals为空, 就新建一个字典对象
  if (locals == NULL) {
    locals = f->f_locals = PyDict_New(); 
    if (locals == NULL) {
      PyErr_Clear(); /* Can't report it :-( */
      return;
    }
  }
  
  co = f->f_code;
  map = co->co_varnames;
  if (!PyTuple_Check(map))
    return;
  PyErr_Fetch(&error_type, &error_value, &error_traceback);
  fast = f->f_localsplus;
  j = PyTuple_GET_SIZE(map);
  if (j > co->co_nlocals)
    j = co->co_nlocals;
    
  // 将 f_localsplus 写入 locals
  if (co->co_nlocals)
    map_to_dict(map, j, locals, fast, 0);
  ncells = PyTuple_GET_SIZE(co->co_cellvars);
  nfreevars = PyTuple_GET_SIZE(co->co_freevars);
  if (ncells || nfreevars) {
    // 将 co_cellvars 写入 locals
    map_to_dict(co->co_cellvars, ncells,
          locals, fast + co->co_nlocals, 1);
          
    if (co->co_flags & CO_OPTIMIZED) {
      // 将 co_freevars 写入 locals
      map_to_dict(co->co_freevars, nfreevars,
            locals, fast + co->co_nlocals + ncells, 1);
    }
  }
  PyErr_Restore(error_type, error_value, error_traceback);
}