closest node to specific node

hi,

    I am a new abaqus python scripting user. I am working parametric study on  Plate with perforations with free meshed technique. I used :myNodes = allNodes.getByBoundingBox(xmin, ymin, zmin, xmax, ymax, zmax) for selecting nodes  but how can it be for selecting  the closest one node  to specific node which has (x,y,z)? please help