Can't put Python listing in LaTeX - latex

Question

I'm trying to put a Python listing into a \fbox\parbox but I always get errors.
Here is my code:
\documentclass[12pt]{article}
% Packages
\usepackage[utf8]{inputenc} % support for accents
\usepackage[T1]{fontenc}
\usepackage[francais]{babel} % doc language
\usepackage{lmodern}
\usepackage[a4paper]{geometry} % marges
\usepackage{xcolor} % text color
\usepackage{sectsty} % colorize sections
\usepackage{changepage}
\usepackage{moreverb} % code with indent
\usepackage{listings} % display code with magnification
\usepackage{amssymb}
\usepackage{amsmath} % Text into equation
\usepackage{enumitem} % Continue enumerate numbers
\usepackage{fourier} % Double brackets
% Python listing
\newcommand\pythonstyle{\lstset{
language=Python,
basicstyle=\sffamily,
keywordstyle=\textbf,
commentstyle=\color{blue},
showstringspaces=false,
frame=tb, numbers=left }}
% Python environment
\lstnewenvironment{python}[1][]{
\pythonstyle \lstset{#1} }{}
\begin{document}
\begin{enumerate}
\item On suppose qu'on dispose d'une fonction \texttt{binom(n,k)}, prenant en entrée deux entiers, et qui calcule $\binom{n}{k}$. Ecrire en langage \textsc{Python} une fonction \texttt{bernoulli(n)}, qui prend en entrée un entier naturel, et qui renvoie la liste \texttt{[b\_0, b\_1, ..., b\_n]}. \par
\fbox{\parbox{\linewidth-2\fboxrule-2\fboxsep}{
La relation précédente donne, pour $n \ge 2$ :
\[ \binom{n}{n-1} b_{n-1} = - \sum_{j=0}^{n-2} \binom{n}{j} b_j \]
autrement dit on a la relation de récurrence, pour tout $m \ge 1$ :
\[ b_m = -\frac{1}{m+1} \sum_{j=0}^{m-1} \binom{n}{j} b_j \]
On en déduit le code demandé :
}}
\fbox{\parbox{\linewidth-2\fboxrule-2\fboxsep}{
\begin{python}
def bernoulli(n) :
liste_bj = [1]
for m in range(1,n+1):
b = 0
for j in range(m):
b -= binom(m+1,j) * liste_bj[j]
b /= m+1
liste_bj.append(b)
return liste_bj
\end{python}
}} %err1
\end{enumerate}
I got the following errors:
On documentclass : Emergency stop, Fatal error occured, no output PDF produced!
On err1 : Argument of \lst#next has an extra }. Paragraph ended before \lst#next was complete. Extra }, or forgotten \endgroup
On \end{enumerate} : \begin{python} ended by \end{enumerate}
On \end{document} : \begin{enumerate} ended by \end{document}. You can't use '\end' in internal vertical mode. Missing { inserted
I tried to erase the "python listing" and "python environment" on the preamble and replace \begin{python} with \begin{listings} (same with \end) to reset my LaTeX project with the standard presentation of code, but I still get the same errors. So it seems that LaTeX has trouble to read that my listing closure command is put before closing the enumerate one. Maybe it's because I put the listing into a \fbox\parbox?
The \fbox\parbox works well with text and equations in it, so the issue does not come from there.

Answer 1

You must not use fragile content, such as listings, as argument of other macros.
Anyway, the fbox\parbox is really superfluous - lstings has a frame option for this:
\documentclass[12pt]{article}
% Packages
\usepackage[utf8]{inputenc} % support for accents
\usepackage[T1]{fontenc}
\usepackage[french]{babel} % doc language
\usepackage{lmodern}
\usepackage[a4paper]{geometry} % marges
\usepackage{xcolor} % text color
\usepackage{sectsty} % colorize sections
\usepackage{changepage}
\usepackage{moreverb} % code with indent
\usepackage{listings} % display code with magnification
\usepackage{amssymb}
\usepackage{amsmath} % Text into equation
\usepackage{enumitem} % Continue enumerate numbers
\usepackage{fourier} % Double brackets
% Python listing
\newcommand\pythonstyle{\lstset{
language=Python,
basicstyle=\sffamily,
keywordstyle=\textbf,
commentstyle=\color{blue},
showstringspaces=false,
frame=tb, numbers=left }}
% Python environment
\lstnewenvironment{python}[1][]{
\pythonstyle \lstset{#1} }{}
\begin{document}
\begin{enumerate}
\item On suppose qu'on dispose d'une fonction \texttt{binom(n,k)}, prenant en entrée deux entiers, et qui calcule $\binom{n}{k}$. Ecrire en langage \textsc{Python} une fonction \texttt{bernoulli(n)}, qui prend en entrée un entier naturel, et qui renvoie la liste \texttt{[b\_0, b\_1, ..., b\_n]}. \par
\fbox{\parbox{\linewidth-2\fboxrule-2\fboxsep}{
La relation précédente donne, pour $n \ge 2$ :
\[ \binom{n}{n-1} b_{n-1} = - \sum_{j=0}^{n-2} \binom{n}{j} b_j \]
autrement dit on a la relation de récurrence, pour tout $m \ge 1$ :
\[ b_m = -\frac{1}{m+1} \sum_{j=0}^{m-1} \binom{n}{j} b_j \]
On en déduit le code demandé :
}}
% \fbox{\parbox{\linewidth-2\fboxrule-2\fboxsep}{
\begin{python}[frame=single,linewidth=1.035\linewidth]
def bernoulli(n) :
liste_bj = [1]
for m in range(1,n+1):
b = 0
for j in range(m):
b -= binom(m+1,j) * liste_bj[j]
b /= m+1
liste_bj.append(b)
return liste_bj
\end{python}
% }} %err1
\end{enumerate}
\end{document}
(and \end{document} was obviously missing)