looping through splines of a bezier circle, can only find 1 spline not 4 I'm trying to port differential line growth to blender animation nodes following this example https://vimeo.com/169438763 .
I was suggested to work with splines in blender as it would be a lot simpler to working directly with meshes.

Right now I'm trying to create a function that loops through every spline of a bezier circle, and add a spline in between two splines when the distance between these two splines is larger than X.

To this effect I'm looping throughout the splines of the bezier circle but the problem I'm hitting is that the loop only finds one element. Shouldn't it find 4 as indicated in edit mode ?
Your object has curve data. The curve data object holds a spline collection.

In each spline there are bezier_points or points.

You have mistaken a bezier point for a spline. The spline is a continued element made up from multiple points. As a curve data object can hold multiple splines (they can be discontinued/separate), it has a spline collection.

You can access the points with the Spline Info node. However if you want to produce a variable point list, I'd suggest inserting a script node which takes in a point list and outputs the modified point list.