Setting variable to search cursors to calculate percent using ArcPy?

Question

I made a Python script tool and to finish my script I want to perform a percentage calculation using the 2 results from my search cursors. And the print the result to screen.

Here's what I have (but not working):

# Run search cursor on areas with slope code 3
with arcpy.da.SearchCursor(shapecalc_input, ['POLY_AREA'], "SlopeCode in (3)") as cur1:
     sum = 0    
     for row in cur1:     
       sum += row[0]    

arcpy.AddMessage(sum)

# Run search cursor on areas with slope code 1 and 2
with arcpy.da.SearchCursor(shapecalc_input, ['POLY_AREA'], "SlopeCode in (1, 2)") as cur2:
     sum = 0    
     for row in cur2:     
       sum += row[0]    

arcpy.AddMessage(sum)

arcpy.AddMessage((cur1/cur2)*100)

My search cursors give me the right values, just the calculation isn't working (last line).

Is my syntax wrong? or should I be using a different method completely? I'm new to Python.

Answer 1

You are overwriting the sum variable with your 2nd cursor which you should be using to calculate the percent, not the cursors.

Use:

# Run search cursor on areas with slope code 3
with arcpy.da.SearchCursor(shapecalc_input, ['POLY_AREA'], "SlopeCode in (3)") as cur1:
     sum1 = 0    
     for row in cur1:     
         sum1 += row[0]    

# Run search cursor on areas with slope code 1 and 2
with arcpy.da.SearchCursor(shapecalc_input, ['POLY_AREA'], "SlopeCode in (1, 2)") as cur2:
     sum2 = 0    
     for row in cur2:     
         sum2 += row[0]    

arcpy.AddMessage((sum1/sum2)*100)

Or with a single cursor:

# Run search cursor on areas with slope code 1, 2 or 3
with arcpy.da.SearchCursor(shapecalc_input, ['POLY_AREA', 'SlopeCode'], "SlopeCode in (1, 2, 3)") as cur:
     sum1 = sum2 = 0    
     for row in cur:     
         if row[1] == 3:
             sum1 += row[0]
         else:
             sum2 += row[0]

arcpy.AddMessage((sum1/sum2)*100)

One note: it would be simpler to leave your slope classification in raster to calculate the area.