Adding programming code into LaTex / LyX

My favorite environment for this minted. I use it to input entire source files such as:

\inputminted[linenos,fontsize=\scriptsize]{python}{script.py}

You can also use it without inputing a file, and more importantly, define how much indent it gobbles once pasted:

\newminted{python}{gobble=4,linenos,fontsize=\scriptsize}
\begin{pythoncode}
    print('I am a Python script')
\end{pythoncode}

That way your LaTeX is still nicely indented, but your verbatim code is not. This also provides syntax-highlighting, which I know you mentioned you weren't interested in. Just don't define the language.

You'll want to use the verbatim environment: http://web.mit.edu/vogt/www/latex/ltx-79.html

If the problem is immediately when you paste it in... are you using an IDE to make the document? Try just opening the file in a plain text editor like gedit or notepad.

I'd go with minted, as fideli suggested, but it's good to be aware of the listings package, which is a pure Latex solution ot the problem.

minted is derived from Pygments, a source highlighter written in Python. minted coimes with a Latex bridge, based on \write18, and the texments package provides one for Pygments. There's no downside to minted compared to Pygments that I know of: maybe the two will be merged at some point.