python 源代码中遇到一个变量名 PyId_stdout，搜不到在哪里定义的，如下只能搜到引用的位置（python3.8.10）：

找了半天发现是用宏来构造的声明语句：

// filepath: Include/cpython/object.h
typedef struct _Py_Identifier {
    struct _Py_Identifier *next;
    const char* string;
    PyObject *object;
} _Py_Identifier;

#define _Py_static_string_init(value) { .next = NULL, .string = value, .object = NULL }
#define _Py_static_string(varname, value)  static _Py_Identifier varname = _Py_static_string_init(value)
#define _Py_IDENTIFIER(varname) _Py_static_string(PyId_##varname, #varname)

实际定义 PyId_stdout 的位置在：

// filepath: Python/pythonrun.c
_Py_IDENTIFIER(builtins);
_Py_IDENTIFIER(excepthook);
_Py_IDENTIFIER(flush);
_Py_IDENTIFIER(last_traceback);
_Py_IDENTIFIER(last_type);
_Py_IDENTIFIER(last_value);
_Py_IDENTIFIER(ps1);
_Py_IDENTIFIER(ps2);
_Py_IDENTIFIER(stdin);
_Py_IDENTIFIER(stdout);
_Py_IDENTIFIER(stderr);
_Py_static_string(PyId_string, "<string>");