If you want to do full-screen applications with no windows involved and use Python over C, you have several options:

Game engines: For example the SDL library. Python bindings exist here.
SDL applications run on top of X, wayland, framebuffer, SVGALib and much more. It will give you full-screen graphics and for a SOC you will only need a frame-buffer-device, e.g. when you see the Linux mascot during boot, you are already there. However, if you have some advanced GUI like a modern car cockpit in mind, it might involve OpenGL for anti-aliasing. For an ATM (automatic teller machine) like GUI it will miss the standard buttons and boxes which you would have to implement yourself. Many SDL games in the ubuntu repositiories can be recompiled to run under a framebuffer.

Linux installers: The debian-installer uses the gtk+ toolkit on top of a framebuffer device, no X involved. You will have all Gtk+ widgets at your command, and good text rendering with pango, modern graphics with anti-aliasing with cairo. Python bindings exist. The OpenSuse distribution has a similar installer on top of QT.

Text mode graphics (TUI): If you have only text output with a few buttons to render, consider using the ncurses library. It will allow you a textual user interface with a high-level API. midnight-commander is a good example. Python bindings exist.

Commercial biddings: If this is a professional project, employing other commercial toolkits and realtime operating systems is an option. See also this and similar tagged questions, even without linux at Stack Overflow.

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