2D Laser or Projectile reflection in Pygame

I am stuck on a problem and am actually confused in implementing the logic of that thing.Actually i want to bounce the (say line in pygame) in an enclosed rectangle.By considering the max no of bounces that the line will bounce off and the whole movement of the laser or line will be controlled by holding LeftMouse button and moving around and the angles of line should move! Here is the pic related to that from a unity project! Laser Reflection

Any help will be greatly appreciated! Thankyou