import rhinoscriptsyntax as rs

layers = rs.LayerNames()
splitLayers = []
for layer in layers:
    split = layer.split("::")
    splitLayers.append(split[-1])

for layer in splitLayers:
    ids = rs.ObjectsByLayer(layer)
    if ids:
        selIds = ""
        for id in ids:
            selIds = selIds + "_SelId " + str(id) + " "
        commandString = "-_Export " + selIds + " _Enter " + chr(34) + layer + ".stl" + chr(34) + " _Enter " + "_Enter"
        rs.Command(commandString)