Processing user input as it's entered

[Sven]

Hello,

Is there a way (ideally cross platform but a *nix OS solution would be
great) to process user input as they type?
What I aim to achieve is to count the number of characters a user has
entered and display it while they are typing. The entered text will also
need to be captured once the user has finished typing.

This is a gui-less CLI tool for python 2.7

I've seen some information on tty.setraw but I'm not sure how you'd go
about wiring that up.

Thanks