Flask get viewport size
Rushy already provided a correct answer, but when you want to use flask and bokeh (I am in the same position right now) responsive design does not help in all cases (I am using a bokeh-gridplot and don't want that if accessed from a mobile device). 
I will append "/mobile" to the links from my home page to the plot page on mobile devices (by checking the screen width with css) and then make the plot layout depend on whether "/mobile" was appended to the link. 
Obviously this has some drawbacks (if someone on desktop sends a link to someone on mobile or the other way around), but as my page is login-protected, they will be redirected to the login page in most of the cases anyways (if they are not already logged-in) and need to go to the plot-page manually.
Just in cases this helps someone.
a short question: Is there a way to get my browsers viewport size by Flask?
I'm designing a page for many devices, for example: normal PC, iphone etc...
Thank you, FFodWindow