cfuncdesc environment:

        When processing the optional parameter, don't append any text;
        let the pre-processor supply all of it.

Doc/texinputs/python.sty

@@ -545,7 +545,7 @@
   \begin{fulllineitems}
     \item[\code{#2 \bfcode{#3}(\py@varvars{#4})}\index{#3@{\py@idxcode{#3()}}}]
     \ifx#1\@undefined\else%
-      \emph{Return value: \textbf{#1 reference}.}\\
+      \emph{Return value: \textbf{#1}.}\\
     \fi
 }{\end{fulllineitems}}