There are basically 2 ways to do it.
- Pooling - To put it simply it comes down to browser asking server "Do you have new data for me?" all the time. You can do that with Ajax. All mayor JavaScript libraries have easy to use Ajax functions.
- Realtime - There are 2 ways to do this using JavaScript. Comet approach which usually means long pooling (you request a page from webserver and instead of sending it and closing the connection the server keeps sending data over time and never closes the connection). It's a bit nasty but works. The other way is using HTML5 API WebSockets, which opens a real TCP connection between browser and the server over which you can send your data.
Yes you can use flash, it has something similar to WebSockets. I think it might be even more powerful, but don't quote me on that. But then you'd have to learn Flash and probably make the image/animation in Flash.
Which one to use?
Web before HTML5 wasn't really intended to have realtime connections so all the approaches before HTML5 are more or less hacks, sometimes annoying to deal with and most likely will come with performance hit.
I'd say WebSockets is the way to go if you're just playing around. You'll need a modern browser which supports them though. If you need to support older browsers you'll have to use the other methods.
Flash works, but it requires plugin and most likely won't work on mobile devices. It's also a new language which you need to learn/support. Some people might have it blocked.
Python
If you chose one of the mentioned ways of doing it just Google it adding python keyword. There are quite a lot libraries out there for Python. Same with examples.
The most easiest to implement is probably Ajax pooling since you're just requesting a webpage. Just grab a simple python web framework like Bottle and you'll be ready in no time.
Comet is quite easy as well, but there might be some problems with keeping the connection open for long time and also when you have multiple such connections. You should grab one of the Comet implementations instead of trying to work this out yourself. Take a look at this - Python Comet Server
WebSockets and Flash will require you to write a separate server/script in python which serves the data. There are some available online where you just plug in your logic.