node_ListDropNth.py

import bpy
from node_s import *
from util import *

'''
List skipping allows for a convenient way to drop every nth list element.

This is useful when constructing polygons using 2d lists of vertex indices
where every nth element must be dropped because it would contribute to an
invalid (wrapped around) polygon.

'''


class ListSkipNode(Node, SverchCustomTreeNode):
    ''' List Skip Node '''
    bl_idname = 'ListSkipNode'
    bl_label = 'List Skip'
    bl_icon = 'OUTLINER_OB_EMPTY'

    level = bpy.props.IntProperty(
        name='level_to_Skip', default=2, min=1, update=updateNode)

    typ = bpy.props.StringProperty(name='typ', default='')
    newsock = bpy.props.BoolProperty(name='newsock', default=False)
    skip = bpy.props.IntProperty(name='start', default=0, update=updateNode)

    def draw_buttons(self, context, layout):
        layout.prop(self, "level", text="level")
        layout.prop(self, "skip", text="Skip")

    def init(self, context):
        self.inputs.new('StringsSocket', 'data', 'data')
        self.inputs.new('StringsSocket', 'Skip', 'Skip')

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

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

        if len(outputs['data'].links) == 0:
            return

        if 'data' in inputs and (len(inputs['data'].links) > 0):
            inputsocketname = 'data'
            outputsocketname = ['data']
            changable_sockets(self, inputsocketname, outputsocketname)

            data = SvGetSocketAnyType(self, inputs['data'])
            output = self.skipNth(data, self.level)
            SvSetSocketAnyType(self, 'data', output)

    def skipNth(self, data, level):
        level -= 1
        skip = self.skip
        if level:
            return [self.skipNth(l, level) for l in data]
        elif isinstance(data, (list, tuple)):
            return [i for idx, i in enumerate(data) if (idx-skip) % (skip+1)]
        else:
            return []


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


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


if __name__ == "__main__":
    register()

yes, lets left node not commited. There is enogh stuff in list nodes section.