How to have straight single quotes in lstlistings

You need to load the textcomp package and add upquote=true to your \lstset command. See §4.7 of the listings documentation. Alternatively, you can simply load the upquote package, which will make all verbatim quotes single quotes.

\documentclass{beamer}
\usepackage{listings}
\usepackage{textcomp}
\begin{document}

\lstset{language=Python,upquote=true}
\begin{frame}[fragile]{Code}
\begin{lstlisting}
print 'hi' 
\end{lstlisting}
\end{frame}
\end{document}