src/attr/_make.py

@@ -446,7 +446,11 @@ def _add_init(cls, frozen):
         sha1.hexdigest()
     )
 
-    script, globs = _attrs_to_script(attrs, frozen)
+    script, globs = _attrs_to_script(
+        attrs,
+        frozen,
+        post_init=hasattr(cls, '__post_init__')
+    )
     locs = {}
     bytecode = compile(script, unique_filename, "exec")
     attr_dict = dict((a.name, a) for a in attrs)
@@ -540,7 +544,7 @@ def validate(inst):
             a.validator(inst, a, getattr(inst, a.name))
 
 
-def _attrs_to_script(attrs, frozen):
+def _attrs_to_script(attrs, frozen, post_init=False):
     """
     Return a script of an initializer for *attrs* and a dict of globals.
 
@@ -680,10 +684,8 @@ def fmt_setter_with_converter(attr_name, value_var):
                                                     a.name))
         names_for_globals[val_name] = a.validator
         names_for_globals[attr_name] = a
-    lines.extend([
-        "func = getattr(self, '__post_init__', None)",
-        "if callable(func): func()",
-    ])
+    if post_init:
+        lines.append("self.__post_init__()")
 
     return """\
 def __init__(self, {args}):

tests/test_make.py

@@ -318,6 +318,7 @@ def __post_init__(self2):
         assert hasattr(c, 'z')
         assert c.z == 30
 
+
 @attributes
 class GC(object):
     @attributes