References to specific lines in program source code

Question

How do I make references to specific lines in program source code (e.g. Python)? For example, I want to say:

In lines 22-30, the algorithm is implemented...

If I changed the Python source code, "lines 22-30" will automatically change to reflect the new line numbers.

EDIT:
I'm using minted

Answer 1

I don't use minted, but here's how I would do it for fancyvrb, which minted uses internally. Here, I define new command \VerbLabel{linex}{a $ a} which assigns the label linex to the source code line a $ a.

It's written using expl3, so see the source3 documentation for explanation for any of the commands that don't make sense. In brief: prop in expl3 is a ‘property list’ datatype that holds pair-value data. \prop_gput is the allocator, \prop_if_in tests for the existence of a key, and \prop_get_gdel is an accessor function that also deletes the entry afterwards.

\documentclass{article}
\usepackage{expl3,fancyvrb}
\begin{document}

\ExplSyntaxOn
\cs_generate_variant:Nn \prop_gput:Nnn {Nxn}
\cs_generate_variant:Nn \prop_get_gdel:NnN {NxN}
\cs_generate_variant:Nn \prop_if_in:NnT {NxT}

\prop_new:N \g_verb_label_prop
\newcommand \VerbLabel [2] {
  \prop_gput:Nxn \g_verb_label_prop { \tl_to_str:n {#2} } {#1}
}
\renewcommand \FancyVerbFormatLine [1] {
  #1
  \prop_if_in:NxT \g_verb_label_prop { \tl_to_str:n {#1} }
  {
    \prop_get_gdel:NxN \g_verb_label_prop { \tl_to_str:n {#1} } \l_tmpa_tl
    \label {verbline:\l_tmpa_tl}
  }
}
\ExplSyntaxOff

\VerbLabel{linex}{a $ a}
\VerbLabel{liney}{c & c}

See lines \ref{verbline:linex}--\ref{verbline:liney}

\begin{Verbatim}[numbers=left]
1 _ 1
a $ a
b # b
c & c
9 ^ 9
\end{Verbatim}
\end{document}

There is a bug in this code which means it doesn't work for lines that contain the # char, but that's not an unsolvable problem.

Answer 2

I had the same problem and it was solved by simply putting \labels at the desired lines and then referencing them with \ref. The label is refers the line after which it goes.

Here is an example

\begin{algorithmic}[1]
\FOR {$i$ in 1..10}  \label{alg:loopStart}
    \STATE ...      
\ENDFOR              \label{alg:loopEnd}
\end{algorithmic}

Then I reference the lines like this:

In the loop of the lines \ref{alg:loopStart}-\ref{alg:loopEnd} we make...