Adding copy buttons to code blocks in Sphinx

NOTE: This is now a sphinx extension! Thanks to some friendly suggestions, I’ve written this up as a super tiny sphinx extension. Check it out here: https://github.com/choldgraf/sphinx-copybutton

Sphinx is a fantastic way to build documentation for your Python package. On the Jupyter project, we use it for almost all of our repositories.

A common use for Sphinx is to step people through a chunk of code. For example, in the Zero to JupyterHub for Kubernetes guide we step users through a number of installation and configuration steps.

A common annoyance is that there is a lot of copy/pasting involved. Sometimes you accidentally miss a character or some whitespace. So, I spent a bit of time figuring out how to automatically embed a copy button into code blocks. It turns out this is pretty easy!

Here’s what the final result will look like (just hover the code block below)

wow = this_text
is_so = much*more*copyable

Adding a copy button to your Sphinx code blocks

To accomplish this we’ll use the excellent clipboard.js which provides the machinery for copying the contents of an HTML element as well as jquery for modifying our built documentation on-demand.

The result will be a Sphinx site with code blocks that display a copy button when you hover over them. You can see how it looks on this very page, which uses a similar method (but is built with Jekyll).

Here’s what you should do:

1. Add the clipboard.js javascript. Create a javascript script called doc/_static/custom.js. In the file, put the following code (see comments for explanation):

   function addCopyButtonToCode(){
   // get all code elements
   var allCodeBlocksElements = $( "div.highlight pre" );
   
   // For each element, do the following steps
   allCodeBlocksElements.each(function(ii) {
   // define a unique id for this element and add it
   var currentId = "codeblock" + (ii + 1);
   $(this).attr('id', currentId);
   
   // create a button that's configured for clipboard.js
   // point it to the text that's in this code block
   // add the button just after the text in the code block w/ jquery
   var clipButton = '<button class="btn copybtn" data-clipboard-target="#' + currentId + '"><img src="https://clipboardjs.com/assets/images/clippy.svg" width="13" alt="Copy to clipboard"></button>';
      $(this).after(clipButton);
   });
   
   // tell clipboard.js to look for clicks that match this query
   new Clipboard('.btn');
   }
   
   $(document).ready(function () {
   // Once the DOM is loaded for the page, attach clipboard buttons
   addCopyButtonToCode();
   });
   

2. Add some CSS to make it pretty. Create a custom CSS file called doc/_static/custom.css (or add to one you’ve already got). In the file, put these lines:

   /* Copy buttons */
   button.copybtn {
     webkit-transition: opacity .3s ease-in-out;
     -o-transition: opacity .3s ease-in-out;
     transition: opacity .3s ease-in-out;
     opacity: 0;
     padding: 2px 6px;
     position: absolute;
     right: 4px;
     top: 4px;
   }
   div.highlight:hover .copybtn, div.highlight .copybtn:focus {
       opacity: .3;
   }
   div.highlight .copybtn:hover {
       opacity: 1;
   }
   div.highlight {
       position: relative;
   }
   

3. **Link these scripts in your configuration.** You need to link your
 custom JS and CSS scripts, as well as the clipboard.js script so it ships with
 your site. In your `conf.py` file, add the following function/lines (or add to one you've already
 got defined).

 ```python
 def setup(app):
     app.add_stylesheet('custom.css')
     app.add_javascript("custom.js")
     app.add_javascript("https://cdn.jsdelivr.net/npm/clipboard@1/dist/clipboard.min.js")

And that’s it! Once you clear your Sphinx cache and re-build your site, you should now have buttons that appear when you hover over them, and that copy the text inside when you click them.

Thanks

Many thanks to this StackOverflow post for the majority of the code that led to this hack!

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