Change \code to \verb, because TeX merges the two dashes into a
hyphen, resulting in the output '-list-classifiers', not the correct
'--list-classifiers'. I've verified that the line is now correct
in the DVI, PDF, HTML, and ASCII versions.
diff --git a/Doc/whatsnew/whatsnew23.tex b/Doc/whatsnew/whatsnew23.tex
index 722a7a6..7e3818f 100644
--- a/Doc/whatsnew/whatsnew23.tex
+++ b/Doc/whatsnew/whatsnew23.tex
@@ -757,7 +757,7 @@
\end{verbatim}
The full list of classifiers can be obtained by running
-\code{python setup.py register --list-classifiers}.
+\verb|python setup.py register --list-classifiers|.
\begin{seealso}