Arcpy calculate zero number instead of negative number

Question

I want to develop a model using python.When i want to calculate negative numbers using the model,my script get zero number. Whats wrong in my script ? How can i solve the problem ?

import arcpy
from arcpy import env
env.overwriteOutput = True
env.workspace= r"D:\ppa_test\test.dbf"
arcpy.AddField_management(r"D:\ppa_test\test.dbf",'cf',"Float")
updatecursor = arcpy.UpdateCursor(r"D:\ppa_test\test.dbf",["ppa","pps",'cf'])

for update in updatecursor:
    if update.ppa < update.pps:
        update.cf = (update.ppa - update.pps) / (update.ppa * (1-update.pps))
    elif update.ppa>update.pps:
        update.cf = (update.ppa- update.pps) / (update.pps * (1-update.ppa))
        updatecursor.updateRow(update)
del update
del updatecursor

Answer 1

your updatecursor.updateRow(update) is not well indented, so you only update your row after the elif statement. It should be at the same level as the if and the elif