diff --git a/lib/vast/Nodes.py b/lib/vast/Nodes.py
index 8d8c498..035dd16 100644
--- a/lib/vast/Nodes.py
+++ b/lib/vast/Nodes.py
@@ -11,7 +11,7 @@ AST 树，从而使编译器侧 ``import vast as ast`` 后原有代码零修改
 
 构造语义与 CPython 一致：
 - 位置参数按 ``_fields`` 顺序赋值，超出字段数抛 TypeError
-- 关键字参数全部 setattr（包括未知字段，与 CPython 行为一致）
+- 关键字参数按名赋值（实例为 __slots__ 紧凑布局，仅接受已声明字段）
 - 未传入的字段不设置属性（访问时 AttributeError，与 CPython 一致）
 """
 from __future__ import annotations
@@ -20,6 +20,10 @@ from __future__ import annotations
 class AST:
     """所有 AST 节点的基类（与 ast.AST 同构）。"""
 
+    # 空 __slots__：保证子类定义 __slots__ 后实例不携带 __dict__
+    # （基类若有 __dict__，子类 __slots__ 将失效）
+    __slots__ = ()
+
     _fields: tuple[str, ...] = ()
     _attributes: tuple[str, ...] = ()
 
@@ -310,22 +314,25 @@ def _MakeNodeClass(name: str, fields: tuple[str, ...], attrs: tuple[str, ...]) -
                 f'{name} constructor takes at most {len(fields)} positional arguments'
             )
         for fname, val in zip(fields, args):
-            self.__dict__[fname] = val
+            object.__setattr__(self, fname, val)
         for k, v in kwargs.items():
-            self.__dict__[k] = v
+            object.__setattr__(self, k, v)
 
     base_name: str | None = _BASE_CLASS.get(name)
     base_cls: type = globals()[base_name] if base_name else AST
+    # __slots__ = 位置字段 + 位置属性（实例的全部属性名）
+    slots: tuple[str, ...] = tuple(dict.fromkeys(fields + attrs))
     ns: dict[str, object] = {
         '__init__': _Init,
+        '__slots__': slots,
         '_fields': fields,
         '_attributes': attrs,
+        # 字段默认值不能直接作为类属性（与同名 __slots__ 冲突），
+        # 存入独立类属性供 dump 判断"值为 None 且默认值为 None"时跳过
+        '_node_defaults': dict(_CLASS_DEFAULTS.get(name, {})),
         '__module__': __name__,
         '__doc__': _DOCS.get(name, f'{name} AST 节点（与 ast.{name} 同构）。'),
     }
-    # 类默认值（None 字段在 dump 时跳过）
-    for fname, fdefault in _CLASS_DEFAULTS.get(name, {}).items():
-        ns[fname] = fdefault
     cls: type = type(name, (base_cls,), ns)
     return cls
 
diff --git a/lib/vast/Utils.py b/lib/vast/Utils.py
index 67dc3c7..08e200f 100644
--- a/lib/vast/Utils.py
+++ b/lib/vast/Utils.py
@@ -81,7 +81,7 @@ def dump(node: AST, annotate_fields: bool = True, include_attributes: bool = Fal
                 except AttributeError:
                     keywords = True
                     continue
-                if value is None and getattr(cls, name, ...) is None:
+                if value is None and getattr(cls, '_node_defaults', {}).get(name, ...) is None:
                     keywords = True
                     continue
                 value, simple = _format(value, level)
@@ -96,7 +96,7 @@ def dump(node: AST, annotate_fields: bool = True, include_attributes: bool = Fal
                         value = getattr(node, name)
                     except AttributeError:
                         continue
-                    if value is None and getattr(cls, name, ...) is None:
+                    if value is None and getattr(cls, '_node_defaults', {}).get(name, ...) is None:
                         continue
                     value, simple = _format(value, level)
                     allsimple = allsimple and simple