"$" refers to JQuery, and should be defined in http://docs.python.org/_static/jquery.js.
Maybe you have to import/include that file before http://docs.python.org/_static/copybutton.js?
There are also other js scripts there that use JQuery so I'm not sure why it's failing with the copybutton.

The copy button (the one on the top-right in the code examples) is a fairly new addition and it's not vital for the docs, so if we can't find a solution we can probably just skip that file and build the chm without copy button.