Oops! Forgot the value parameter.

Doc/whatsnew/whatsnew22.tex

@@ -216,7 +216,7 @@ attribute value from \var{object}.
 \item \method{__set__(\var{object}, \var{value})} sets the attribute
 on \var{object} to \var{value}.
 
-\item \method{__delete__(\var{object})} deletes the \var{value} 
+\item \method{__delete__(\var{object}, \var{value})} deletes the \var{value} 
 attribute of \var{object}.
 \end{itemize}