'Too deeply nested' error in `\renewcommand`

Question

I am following this QnA to create a renewed \inputminted command.

\documentclass{article}
\usepackage{minted}                 % code highlighting, uses python pygments
\usepackage{mdframed}
\usepackage{xcolor}
\definecolor{codebg}{rgb}{0.95,0.95,0.95}
\let\inputmintedorig\inputminted    % copy original command [pack:minted]\inputminted to \inputmintedorig
\renewcommand{\inputminted}[3][]{%  % change original \inputminted
    \begin{mdframed}%
        \inputmintedorig[#1]{#2}{#3}%
    \end{mdframed}%
}
\begin{document}
\inputminted[bgcolor=codebg,mathescape,linenos,numbersep=5pt,gobble=2,frame=none,framesep=2mm,label=Some Code]{py}{pycode.py}
\end{document}

where pycode.py contains some arbitray Python code:

  import numpy as np    # importing library
  ls = np.arange(0, 100, 1)

But I am getting error "Too deeply nested. ...framesep=2mm,label=Some Code]{py}{pycode.py}" when using the renewed command. What am I doing wrong?

Answer 1

This is a well-known problem with \let.

When you ask for \show\inputminted you'll be told that

> \inputminted=macro:
->\@protected@testopt \inputminted \\inputminted {}.

The macro doing the real job is \\inputminted (where the second backslash is part of the name. In general, when you have something like

\newcommand{\foo}[2][default]{something with #1 and #2}

LaTeX will internally do something like

\def\foo{\protected@testopt\foo\\foo{default}}
\def\\foo[#1]#2{something with #1 and #2}

but you're not supposed to know it as a user. (Note: I know that the code above isn't what actually LaTeX does, but the details are completely unimportant.)

But you're trying to access internals in order to redefine \inputminted. I believe it's not a good idea, actually. Anyway, when you want to do this you must be aware of the subtleties involved.

With your \let, you're not accessing the real macro that does the job. Worse, the subsequent \renewcommand will clobber the meaning of \\inputminted, so you enter an infinite loop as soon as you use \inputmintedorig.

Until 2021, the correct way to proceed was to load \usepackage{letltxmacro} and say

\LetLtxMacro{\inputmintedorig}{\inputminted}

but now there's a method from the LaTeX kernel itself:

\NewCommandCopy{\inputmintedorig}{\inputminted}

Answer 2

do-it-yourself-way (may be broken if LaTeX kernel change)

\documentclass{article}
\usepackage{minted}
\usepackage{mdframed}
\makeatletter
\expandafter\let\expandafter\inputmintedorig@internal
             \csname\string\inputminted\endcsname
\renewcommand{\inputminted}[3][]{%
\begin{mdframed}%
\inputmintedorig@internal[#1]{#2}{#3}%
\end{mdframed}%
}
\makeatother
\begin{document}
\inputminted{py}{test.py}
\end{document}

But not to be advised, as this may be broken if LaTeX kernel internals change.

By the way doesn't minted documentation explain how to use a "framing" package of one's choice (untested).

use-devoted-package-way

\documentclass{article}
\usepackage{minted}
\usepackage{mdframed}
\usepackage{letltxmacro}
\LetLtxMacro{\inputmintedorig}{\inputminted}
\renewcommand{\inputminted}[3][]{%
\begin{mdframed}%
\inputmintedorig[#1]{#2}{#3}%
\end{mdframed}%
}
\begin{document}
\inputminted{py}{test.py}
\end{document}

The package letltxmacro was created for such tasks.

use-modern-LaTeX-way

copied from egreg answer:

\NewCommandCopy{\inputmintedorig}{\inputminted}