Calculating field in ArcGIS Desktop using ArcPy cursor?

Question

I'm trying to calculate a field based on the values of others in the same layer in a calculation. I can't work out why its not working. I've even cut everything down to just be based on one field and even that won't work, so frustrating!

This is based on one field

rows = arcpy.UpdateCursor(inputFC)
for row in rows:
    val = row.getValue(Infield1)
    row.setValue(outfld , val)
    rows.updateRow(row)
    del rows, row
    arcpy.AddMessage("Completed")

this is the final script. Its meant to calculate calories based on minutes, speed and weight (weight as a number you input rather than a field) import sys, arcpy, math

inputFC = arcpy.GetParameterAsText(0)      # Input feature class
timeField = arcpy.GetParameterAsText(1)      # Input time in minutes
speedField = arcpy.GetParameterAsText(2)      # Input speed
SlopeField = arcpy.GetParameterAsText(3)      # Input Slope
weight = float(arcpy.GetParameterAsText(4))      #input weight in kg


arcpy.AddField_management(inputFC, 'Calories', 'LONG') #create calorie field
rows = arcpy.UpdateCursor(inputFC)
for row in rows:
    time = row.getValue(timeField)
    speed = row.getValue(speedField)
    slope = row.getValue(SlopeField)
    calories = time * (speed * 3.5 * weight)/200 * slope
    row.setValue('Calories', calories)
    rows.updateRow(row)
    del row, rows

this says completed but the calories field ends up being null

Answer 1

Tested using some dummy data and works fine. There were numerous logic problems such as referencing uninitialized variables, using field names instead of field values in calculations, incorrect arguments for setValue, etc.

import arcpy

inputFC = arcpy.GetParameterAsText(0)      # Input feature class
timeField = arcpy.GetParameterAsText(1)      # Name of time field in input feature class
speedField = arcpy.GetParameterAsText(2)      # Name of speed field in input feature class
weight = float(arcpy.GetParameterAsText(3))      # Input weight value in kg

arcpy.AddField_management(inputFC, 'Calories', 'LONG') #create calorie field
rows = arcpy.UpdateCursor(inputFC)
for row in rows:
    time = row.getValue(timeField)
    speed = row.getValue(speedField)
    calories = time * (speed * 3.5 * weight)/200
    row.setValue('Calories', calories)
    rows.updateRow(row)
del row, rows

Answer 2

One solution is to use the field calculator with the logic explained in this question that I asked. Nested "if" statements in ArcGIS Field Calculator

What is the error that you currently get

I think Infield1 * (Infield2 * 3.5 * Infield3)/200
should be calories=Infield1 * (Infield2 * 3.5 * Infield3)/200

as otherwise it seems you are running a calculation but not storing it in a variable.