Groups by Vert count #Blender

blender-groups-by-vert-count.py

import bpy

data = {}
for obj in bpy.data.objects: # bpy.context.selected_objects
    if obj.type == 'MESH':
        data.setdefault(len(obj.data.vertices), []).append(obj)
    
for key, value in data.items():
    group_name = "{} Vertices".format(key)
    
    if group_name not in bpy.data.groups:
        bpy.ops.group.create(name=group_name)
        
    grp = bpy.data.groups.get(group_name)
    for obj in value:
        if len(obj.users_group) == 0:
            grp.objects.link(obj)