BGE: Adding a Python collision API. The initial patch was provided by agoose77, with some edits by me.

KX_GameObject now has a collisionCallbacks list which is a list of callables that are called when a collision occurs. The callables will be called with an argument that contains a reference to the other object involved in the collision (i.e., not self).

doc/python_api/rst/bge_types/bge.types.KX_GameObject.rst

@@ -134,6 +134,12 @@ base class --- :class:`SCA_IObject`
 
       :type: :class:`KX_GameObject` or None
 
+   .. attribute:: collisionCallbacks
+
+      A list of callables to be run when a collision occurs.
+
+      :type: list
+
    .. attribute:: scene
 
       The object's scene. (read-only).