How can I reference lstlisting

Question

I just got the following code.

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{geometry}
\usepackage{blindtext}
\usepackage{enumerate}
\geometry{paper=a4paper, left=24mm, right=23mm, top=20mm, bottom=20mm}
\usepackage{listings}
\lstset{
    basicstyle=\ttfamily\footnotesize,
    xleftmargin=.1\textwidth, 
}
\begin{document}
\blindtext
\begin{lstlisting}[language=Python]
def generate_grid(data, basemap, delta=1):
    grid = {
        'lon': np.arange(-180, 180, delta),
        'lat': np.arange(-89.9,89.9, delta) 
    }
    grid["x"], grid["y"] = np.meshgrid(grid["lon"], grid["lat"])
    grid["x"], grid["y"] = basemap(grid["x"], grid["y"])
    return grid 
\end{lstlisting}
\blindtext
\end{document}

The output looks like this

But I want there to be a number on the left side, because I have several lstlisting and I want to refer to them how do I do that?

(sorry for my drawings)

Answer 1

I combined `listings` and `sidecap` - Side captions for listings and Put text to the right of figures to get the caption to the center right of the listing. Then to add the parentheses the labelformat=parens was used, and to remove the word 'Listing' I used an empty name= option to \DeclareFloatingEnvironment.

Note that the label and caption need to be set in the regular way (so not as lstlisting options) and the parentheses around the \ref statement need to be added manually because labelformat does not extend to the output of \ref.

MWE:

% sources:
% https://tex.stackexchange.com/questions/125106/listings-and-sidecap-side-captions-for-listings
% https://tex.stackexchange.com/questions/49979/put-text-to-the-right-of-figures
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{geometry}
\usepackage{blindtext}
\usepackage{enumerate}
\geometry{paper=a4paper, left=24mm, right=23mm, top=20mm, bottom=20mm}
\usepackage{listings}
\lstset{
    basicstyle=\ttfamily\footnotesize,
    xleftmargin=.1\textwidth, 
}
\usepackage[wide]{sidecap}

\usepackage{caption}
\usepackage{newfloat}
\DeclareFloatingEnvironment[placement={!ht},name=]{listing}
\captionsetup[listing]{labelformat=parens}
\sidecaptionvpos{listing}{c}
\makeatletter
\makeatother
\begin{document}
\blindtext
\begin{SClisting}
 \begin{lstlisting}[language=Python]
def generate_grid(data, basemap, delta=1):
    grid = {
        'lon': np.arange(-180, 180, delta),
        'lat': np.arange(-89.9,89.9, delta) 
    }
    grid["x"], grid["y"] = np.meshgrid(grid["lon"], grid["lat"])
    grid["x"], grid["y"] = basemap(grid["x"], grid["y"])
    return grid 
\end{lstlisting}
\caption{}
\label{lst:grid}
\end{SClisting}
\blindtext
The grid algorithm is described in (\ref{lst:grid}).
\end{document}

Result:

Answer 2

With cleveref and its macro \crefname, you can create a custom counter and assign a label to it--I have added python code for demonstration. Then, with minipage, you could create some space at the right-hand side of the code for a number; I have done it with minipage, which by default aligns a number in the middle.

In the code below, I also suggest a custom environment pythoncode with an optional parameter if for some reason you would like to increase/decrease indentation. Of course, you could parameterise any other option of the environment.

\documentclass{article}
% \usepackage[utf8]{inputenc}
\usepackage{geometry}
\geometry{paper=a4paper, left=24mm, right=23mm, top=20mm, bottom=20mm}
\usepackage{blindtext}
\usepackage{enumerate}
\usepackage{listings}
\lstnewenvironment{pythoncode}[1][.1]{%
  \lstset{
    basicstyle=\ttfamily\footnotesize,
    xleftmargin=#1\textwidth,
    language=Python,
  }}{}
\usepackage[noabbrev]{cleveref}
%%% New counter controlling python code numbers
\newcounter{lst}
\renewcommand*{\thelst}{(\arabic{lst})}   % Format the counter (currently (<number>)
\crefname{lst}{python code}{python codes} % Adds a label when referencing
\AtBeginEnvironment{minipage}{\noindent}  % Removes indentation at the beginning of each minipage
\begin{document}
\blindtext
\begin{minipage}{\dimexpr\textwidth-3em}%
  \refstepcounter{lst}\label{lst:a}%
  \begin{pythoncode}
def generate_grid(data, basemap, delta=1):
grid = {
  'lon': np.arange(-180, 180, delta),
  'lat': np.arange(-89.9,89.9, delta) 
}
grid["x"], grid["y"] = np.meshgrid(grid["lon"], grid["lat"])
grid["x"], grid["y"] = basemap(grid["x"], grid["y"])
return grid
  \end{pythoncode}%
\end{minipage}{\raggedleft\thelst\par}
\blindtext
\begin{minipage}{\dimexpr\textwidth-3em}
  \refstepcounter{lst}\label{lst:b}%
  \begin{pythoncode}
def foo(x):
    return x**2
  \end{pythoncode}
\end{minipage}{\raggedleft\thelst\par}
\Cref{lst:a} and \cref{lst:b}.
\end{document}