More fiddling with padding and size for messages which do not fit in the slide.

doc/nextml2015/presentation.tex

@@ -720,6 +720,8 @@ Backtrace when the node is created:
 \lstset{language=Python,
         commentstyle=\itshape\color{blue},
         stringstyle=\color{violet},
+        basicstyle=\footnotesize,
+        xleftmargin=-1em
         }
 \begin{lstlisting}
 Traceback (most recent call last):