import arcpy, os, sys

InFolder = sys.argv[1] # folder for shapefiles, or database for feature classes

arcpy.env.workspace = InFolder

for ThisFC in arcpy.ListFeatureClasses():
    # assuming any field with an underscore needs to be split
    SplitFields = arcpy.ListFields(ThisFC,"*_*")
    # iterate through each field found with an underscore
    for ThisField in SplitFields:
        # skip shape length and shape area fields
        if not ThisField.baseName.lower() == "shape_length" and not ThisField.baseName.lower() == "shape_area" :
            # break it up into parts
            Parts = ThisField.baseName.split("_")
            for ThisPart in Parts:
                # Add a field for each part
                arcpy.AddField_management(ThisFC,ThisPart,"TEXT",field_length = 30)
                # populate with the part (""" is a quote). In order to put a string into
                # a field it is necessary to quote it so the processor understands that it's
                # a string to be populated and not a field name.
                arcpy.CalculateField_management(ThisFC,ThisPart,""" + ThisPart + ""","PYTHON")