image = gimp.image_list()[0] for layer in image.layers: oname = layer.name front = oname.split('(')[0] + '(' ms = (oname.split('(')[1]).split(')')[0][:-2] back = 'ms)' + (oname.split('ms)'))[-1] newms = str(int(int(ms)/3)) layer.name = front+newms+back