Symbols replaced with not working ones into Python codes written via lstlisting Latex

Question

lstlisting looks working great on python scripts except for some signs. From my experience the symbols "-" and "*" are replaced with something else, very similar in shape, but different. As a result the script reported into the pdf file doesn't work. That's the problem we are dealing with.

Here a simple sample code we gonna use in order to deal with this issue:

\documentclass{article}

\usepackage{listings}


\begin{document}
\lstset{language=Python}
\lstset{frame=lines}
\lstset{caption={Insert code directly in your document}}
\lstset{label={lst:code_direct}}
\lstset{basicstyle=\footnotesize}
%\lstset{keepspaces=true}
\lstset{columns=fullflexible}
\begin{lstlisting}
import numpy as np
import matplotlib.pyplot as plt
x = np.arange(-3, 3, 0.01)
y = np.sin(np.pi*x)/(np.pi*x)

plt.plot(x, y)
\end{lstlisting}


\end{document}

When I run it a pdf file is generated which looks great

import numpy as np
import matplotlib.pyplot as plt
x = np.arange(−3, 3, 0.01)
y = np.sin(np.pi∗x)/(np.pi∗x)
plt.plot(x, y)

However, if I try to copy and paste this code on a Python intepreter I realize it does not work, as "*" and "-" are replaced with something else, very similar in shape, but different. Could you help me to fix it, please?

Answer 1

Not totally clear to me why this happens... can you add your preamble to the code? In particular, I am wondering what encoding (inutenc) you use.

Not sure why listings behaves this way, but I found a literate option that allows specifying characters that should get replaced in the listing. In this case, I replace the minus with a minus, which seems to prevent some other code from replacing it with a different character. (I always got an equals sign.)

This works for me:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{listings}
\begin{document}

\lstset{language=Python, literate={-}{-}1}
\lstset{frame=lines}
\lstset{caption={Insert code directly in your document}}
\lstset{label={lst:code_direct}}
\lstset{basicstyle=\footnotesize}
\lstset{keepspaces=true}
\lstset{columns=fullflexible}

\begin{lstlisting}
import numpy as np
import matplotlib.pyplot as plt
x = np.arange(-3, 3, 0.01)
y = np.sin(np.pi*x)/(np.pi*x)

plt.plot(x, y)
\end{lstlisting}

\end{document}

Inspired by this question on tex.stackexchange.com.

Answer 2

As suggested, the solution for this issue is to make listings NOT replacing some particular signs, in this case "*" and "-". This means that the line of code

\lstset{language=Python}

needs to be replaced with

\lstset{language=Python, literate={symbol_1}{symbol_l}1 {symbol_2}{simbol_2}1 }

where we are assuming we have two symbols which are in some ways mistakenly replaced: "symbol_1" and "symbol_2"

So, in order to have a Latex sample code which generates a pdf with a fully working Python code, the previously sample code needs to be replaced with what follows:

\documentclass{article}

\usepackage{listings}


\begin{document}
\lstset{language=Python, literate={-}{-}1 {*}{*}1}
\lstset{frame=lines}
\lstset{caption={Insert code directly in your document}}
\lstset{label={lst:code_direct}}
\lstset{basicstyle=\footnotesize}
%\lstset{keepspaces=true}
\lstset{columns=fullflexible}
\begin{lstlisting}
import numpy as np
import matplotlib.pyplot as plt
x = np.arange(-3, 3, 0.01)
y = np.sin(np.pi*x)/(np.pi*x)

plt.plot(x, y)
\end{lstlisting}


\end{document}

I do not guarantee it's going to work for each Python code, but each time you test a Python code or similar, copied and pasted from a Latex generated script, you may be able to fix an incoming bug just by adding literate={symbol_x}{symbol_x}1, as I did before