Hi everyone!
I would like to make an Air Hockey game in pygame.
I was wondering if it was possible to have 'proper' bouncing (ie. the puck goes in a direction relative to the angle the paddle hit it in).
I can easily write the rest of the code.

Most pygame tutorial give you an implementation of simple bouncing. An ideal round ball hits on an ideal straight wall without spinning and losing energy.

I am not sure I know what an air hockey game is. The only difference I can think of, can be the spin of the ball or curve like surfaces or deformation of bodies.

You must add the paddle's momentary velocity to the pucks velocity*-1 in a vectorial way.
That means if the paddle is not moving, then the velocity of the puck after the hit is -1*velocity before the hit. As expected.

If you have the velocity vector you have the angle of it.

If the puck comes in with the velocity vector (-1,-2), and the paddle is moving with (3,4), then the velocity vector of the puck will be -1*(-1,-2)+(3,4)==(4,6)
The angle of (4,6) is arcus tangent (6/4), or any other arcus trigonometric function can be used.