[3.13] Programming FAQ: Mention object.__setattr__ as a technique for delegation (GH-124617) (#124624)

miss-islington · JelleZijlstra · web-flow · commit ce63ea0fe42b · 2024-09-26T13:55:08.000-07:00
Programming FAQ: Mention object.__setattr__ as a technique for delegation (GH-124617) This is used for example by threading.local in the stdlib. (cherry picked from commit 43979fa) Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
diff --git a/Doc/faq/programming.rst b/Doc/faq/programming.rst
@@ -1613,9 +1613,16 @@ method too, and it must do so carefully.  The basic implementation of
            self.__dict__[name] = value
        ...
 
-Most :meth:`!__setattr__` implementations must modify
-:attr:`self.__dict__ <object.__dict__>` to store
-local state for self without causing an infinite recursion.
+Many :meth:`~object.__setattr__` implementations call :meth:`!object.__setattr__` to set
+an attribute on self without causing infinite recursion::
+
+   class X:
+       def __setattr__(self, name, value):
+           # Custom logic here...
+           object.__setattr__(self, name, value)
+
+Alternatively, it is possible to set attributes by inserting
+entries into :attr:`self.__dict__ <object.__dict__>` directly.
 
 
 How do I call a method defined in a base class from a derived class that extends it?
