If you're just too lazy to indent a huge number of lines, you can select it and click on the {}-button in the panel above the text field where you enter your post.
Another possibility is to use the HTML tag pair <pre> ... </pre> for code formatting. It means "preformatted text" and looks the same as code blocks indented with 4 spaces.
Example (written with indentation to escape the HTML tag and make it visible!):
<pre>
# Here come some code lines
# ...
exit
</pre>