Embed Flask page in another without code duplication?
To re-use a chunk of HTML, you can use Jinja's {% include %} tag. If that's too limiting, Jinja macros are also well suited. You can define your macros in a separate file and import them with {% import "path/to/macros.html" as my_macros %}.
Flask-Assets can help with the organisation of your assets.
As for using Blueprints, yes you should use them. But they mostly apply to Python code and HTML templates are organised in a different realm, so maybe their use is unrelated here.
You can't always remove all duplication though. If your game needs to affect three distant locations of the server-generated HTML, that's bits of template code to copy in every template that includes your game.
I have a page (located at /games/compare/) and it's a mini image comparison game. Users are shown two images and asked to pick between them in response to a question. This page can get images from the database, render a template with javascript and css inside and communicate back to the database using AJAX.
Now what if I wanted to embed this voting game onto the main page without duplicating any code? Ideally, I'd update the game and all the pages that "feature" the game will also reflect the changes.
I'm getting hung up on how to manage the assets for the entire site in a coherent and organized way. Some pages have css, javascript and I'm also using frameworks like bootstrap and a GIS framework.
Would I set the game up as a blueprint? How would I organize the assets (Javascript and CSS) so that there is no duplication?
Currently, I have a page rendering a template (main.html) which extends another (base.html). Base.html includes header.html, nav.html and footer.html with blocks set up for body and others.
My current approach is to strip everything out at the lowest level and reassemble it at a highest common level, which makes coding really slow. For instance, I have that voting game and right now it's located in a page called voting_game.html and has everything in it needed to play the game (full page html, styles and javascript included). Now if I want to include that game on another page, like the root index, the only solution I know of is to strip out the style, js and full page html from voting_game.html, leaving only the html necessary for the game to run. When I'm creating the index now, I'll import the html from voting_game.html but I'll separately have to import the style and javascript. This means I have to build every page twice, which is twice the work I need to be doing. This process also leaves little files all over the place, as I'm constantly refactoring and it makes development just a bookkeeping nightmare. 
There has to be a way to do this and stay organized but I need your help understanding the best way to do this.
Thanks,
Phil
Edit: The embedded page should also be able to communicate with its parent page (the one it is being embedded into), or with other embedded pages within the same parent (children of a parent should be able to talk. So when someone plays the embedded game, they earn points, which should show up on another part other page, which would update reflecting the users current points.
This "Score board" would also be a separate widget/page/blueprint that can be embedded and will look for certain pieces of data in order to function.