Testing scenario is, 


creating a cell, 
Change the language from the drop down menu(from R to Python), 
Enter the code and execute it. HTML code for drop down menu is




&lt;select class="form-control cell-control-select cell-control"&gt;
    &lt;option&gt;Markdown&lt;/option&gt;
    &lt;option&gt;R&lt;/option&gt;
    &lt;option&gt;Python&lt;/option&gt;
    &lt;option&gt;RMarkdown&lt;/option&gt;
&lt;/select&gt;


and below is my casperjs code

casper.then(function(){
    this.mouse.click({ type: 'xpath' , path: "/html/body/div[3]/div/div[2]/div/div[3]/div[1]/div/select"});//x path for dropdown menu
    this.echo('clicking on dropdown menu');
    this.wait(3000);
});

casper.then(function(){
    var z = this.evaluate(function() {
    document.querySelector('.form-control').selectedIndex = 2;
    return true;
    });
    this.wait(3000);
});


it is selecting the Python language from the drop down menu but when we run the code it is showing Error in prompt cell. The same error we get when we run R code in python language cell.


Question: Need directions regarding the learning process I should follow for learning Photoshop
Answer: Personally, I find that Illustrator (with pixel preview and align to pixel grid) has been much more useful than Photoshop in a web workflow. Artboards are intuitively helpful when designing for multiple output devices, the Pathfinder panel allows you to create more nuanced objects, and the Symbols palette allows you to develop more modularity in your approach to asset creation. Modularity = rapid development = the way to go in the current industry environment.  Plus, the way Illustrator handles layers and stacking order is more simple than Photoshop's Layers panel.

I apologize for slightly derailing the question, but I feel that Illustrator is a tool much better suited for web work than Photoshop—it's more maintainable and intuitive, once you've gotten past the initial unfamiliarity that comes from working with vector files instead of raster files. I think the links I've provided will serve as a pretty good primer for getting yourself situated with using Illustrator as an alternative to Photoshop for web development.