python engine ....

You don't need an 'engine' to build games (after all, you've been able to build quite a few so far, haven't you?), you simply need some core functionality like rendering, input handling, sound playing, etc, which is where frameworks like Pygame or Pyglet come in handy.

So, what's the real issue here? You want reusable code? Look at the games you've built so far and see what things they had in common and what things could've been generalized a bit more.

An "engine" is a popular name for the pre-integration of graphics, input, sound, networking, serialization and other interfaces for the purpose of implementing a specific game. It can be a simple collection of relatively low-level routines, a library coupled with a few extension/convenience functions, or a large number of sophisticated software facilities tuned to interoperate with each other. The identifying characteristic of an "engine" is that you simply need to provide data to it to complete the game.

You want to make a Street Fighter 2 style game. You need graphics, obviously, as well as sound, input handling and data services. You need behavioral logic to guide your fighters, including patterns of behavior and the ability to recognize user patterns by analyzing input history (in the current match, across rounds) and identify an advantageous strategy. You need a framework to handle hitboxes spread across the fighter's body in all possible stances, indicating relative damage amounts, stun effects and attack susceptibility (blocking).

Put that together and you have your engine.