node_KDTreeEdges.py

from node_s import *
from util import *
from mathutils import Vector, kdtree
import bpy

# documentation/blender_python_api_2_70_release/mathutils.kdtree.html


class SvKDTreeEdgesNode(Node, SverchCustomTreeNode):

    bl_idname = 'SvKDTreeEdgesNode'
    bl_label = 'Kdtree Edges'
    bl_icon = 'OUTLINER_OB_EMPTY'

    def draw_buttons(self, context, layout):
        pass

    def init(self, context):
        self.inputs.new('VerticesSocket', 'Verts', 'Verts')
        self.inputs.new('StringsSocket', 'minDistance', 'minDistance')
        self.inputs.new('StringsSocket', 'maxDistance', 'maxDistance')
        self.inputs.new('StringsSocket', 'maxNum', 'maxNum')

        self.outputs.new('StringsSocket', 'Edges', 'Edges')

    def update(self):
        inputs = self.inputs
        outputs = self.outputs

        # if not ('Verts' in inputs and inputs['Verts'].links):
        #     return

        try:
            verts = SvGetSocketAnyType(self, inputs['Verts'])[0]
            mindist = SvGetSocketAnyType(self, inputs['minDistance'])[0][0]
            maxdist = SvGetSocketAnyType(self, inputs['maxDistance'])[0][0]
            maxNum = SvGetSocketAnyType(self, inputs['maxNum'])[0][0]
            # print(mindist, maxdist)
            linked = outputs[0].links
        except (IndexError, KeyError) as e:
            return

        # make kdtree
        # documentation/blender_python_api_2_70_release/mathutils.kdtree.html
        size = len(verts)
        kd = mathutils.kdtree.KDTree(size)

        for i, vtx in enumerate(verts):
            kd.insert(Vector(vtx), i)
        kd.balance()

        # makes edges
        e = []
        maxNum = max(maxNum, 1)
        for i, vtx in enumerate(verts):
            num_edges = 0
            for (co, index, dist) in kd.find_range(vtx, maxdist):
                if i == index or (num_edges > maxNum):
                    continue
                if dist < mindist:
                    continue
                e.append([i, index])
                num_edges += 1

        SvSetSocketAnyType(self, 'Edges', e)

    def update_socket(self, context):
        self.update()


def register():
    bpy.utils.register_class(SvKDTreeEdgesNode)


def unregister():
    bpy.utils.unregister_class(SvKDTreeEdgesNode)

if __name__ == "__main__":
    register()

A set can't have lists as members since they are mutable. Afterwards we can use list(map(list,e)) to change to lists