\documentclass{article}
\usepackage{pgffor}

\newcommand{\MyInclude}[1]
{
   File
   \IfFileExists{#1}
   {
      #1 contents: \input{#1}
   }{
      non-existent: #1
   }   
}

\newcommand{\MyListing}[1]
{
   \begin{itemize}
      \foreach \itm in #1
      {
         \item{\MyInclude{\itm}}
      }
   \end{itemize}
}

\begin{document}
   \newcommand{\MyList}{
      1,2,3,
      Section.1.tex,
      Section.2.tex,
      Section.3.tex,
   }

   \MyListing{\MyList}
   
   
\end{document}
