Can't put Python listing in LaTeX

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.

Solution

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)