I need to write a python script which opens a website and when the website is completly opened it takes a screenshot of the opened website.
I wrote sth like this:
I believe that you need different solutions for different operating systems. Use sys.platform to find out on which platform you are on. The rest you have to figure out yourself, but a quick internet search revealed:
Take a screenshot via a python script. [Linux]
Fastest way to take a screenshot with python on windows
Take screenshot in Python on Mac OS X
This solution is fairly cross-platform, but if you're trying to show a bit of a web page open in a desktop with menu/toolbars etc... it's not what you want.
You could use SeleniumHQ to automate a browser of your choice, have that browser render the page, then get the complete image of the rendered page - ie, not just a screenshot of the portion of the page that's displayed on screen. You could then crop that accordingly.
According to this question, you should be able to use ImageGrab to take a screenshot. Since ImageGrab uses PIL, this should be cross-platform. Here is some sample code to get you on your way
Hope this helps