Selenium Find By X path Errror

I am new to Selenium and was trying to scrape YouTube. But I encountered a weird problem. I was trying to scrape the following:

http://ift.tt/2xZEpg4

And this is my code:

http://ift.tt/2yJbHUt

When I do this in the interactive shell then it works fine but when I rerun the script after saving it then it shows me an error saying the element can't be found. What is that I am missing. Please Help