I have created a simple arcpy script to add four fields (name, shapeArea, shapeLen, quantile) to a layer and to compute the values of shapeArea and shapeLen. Because I need to do this for a number of features, the input is a group layer rather than a feature. My problem is that the program will only do only one of the additions at a time and then fail. Because I test if the field to be added already exists, I can get through it by running the script four times. However, that obviously is not ideal. Can anyone tell me what I am doing wrong?