documentclass{article}
usepackage{listings}
usepackage{amsmath}
lstdefinestyle{mystyle}{
  basicstyle=ttfamily,
  mathescape
}
begin{document}
bgroup
  begin{lstlisting}[style=mystyle]
    $displaystyleleft(sum_itext{ttfamily my_var}right)$:
    $texttt{my_var}neq$ my_var because $texttt_neq$_
  end{lstlisting}
egroup
end{document}