How to change font size on part of the page in LaTeX?

\begingroup
    \fontsize{10pt}{12pt}\selectfont
    \begin{verbatim}  
        % how to set font size here to 10 px ?  
    \end{verbatim}  
\endgroup

The use of the package \usepackage{fancyvrb} allows the definition of the fontsize argument inside Verbatim:

\begin{Verbatim}[fontsize=\small]
print "Hello, World"
\end{Verbatim}

The fontsize that you can specify are the common

\tiny 
\scriptsize  
\footnotesize 
\small
\normalsize
\large
\Large
\LARGE
\huge
\Huge

Example:

\Large\begin{verbatim}
   <how to set font size here to 10 px ? />
\end{verbatim}
\normalsize

\Large can be obviously substituted by one of:

\tiny
\scriptsize
\footnotesize
\small
\normalsize
\large
\Large
\LARGE
\huge
\Huge

If you need arbitrary font sizes:

• How can I get an arbitrary font size in LaTeX?