fix: avoid multiple calls of __post_init__ when dataclasses are inherited

changes/4487-PrettyWood.md

@@ -0,0 +1 @@
+fix: avoid multiple calls of `__post_init__` when dataclasses are inherited

pydantic/dataclasses.py

@@ -285,7 +285,10 @@ def handle_extra_init(self: 'Dataclass', *args: Any, **kwargs: Any) -> None:
             init(self, *args, **kwargs)
 
     if hasattr(dc_cls, '__post_init__'):
-        post_init = dc_cls.__post_init__
+        try:
+            post_init = dc_cls.__post_init__.__wrapped__  # type: ignore[attr-defined]
+        except AttributeError:
+            post_init = dc_cls.__post_init__
 
         @wraps(post_init)
         def new_post_init(self: 'Dataclass', *args: Any, **kwargs: Any) -> None:

tests/test_dataclasses.py

@@ -1472,3 +1472,28 @@ def __post_init__(self):
             self.a *= 3
 
     assert C().a == 6  # 1 * 3 + 3
+
+
+def test_inheritance_post_init_2():
+    post_init_calls = 0
+    post_init_post_parse_calls = 0
+
+    @pydantic.dataclasses.dataclass
+    class BaseClass:
+        def __post_init__(self):
+            nonlocal post_init_calls
+            post_init_calls += 1
+
+    @pydantic.dataclasses.dataclass
+    class AbstractClass(BaseClass):
+        pass
+
+    @pydantic.dataclasses.dataclass
+    class ConcreteClass(AbstractClass):
+        def __post_init_post_parse__(self):
+            nonlocal post_init_post_parse_calls
+            post_init_post_parse_calls += 1
+
+    ConcreteClass()
+    assert post_init_calls == 1
+    assert post_init_post_parse_calls == 1