Calculate geometry with Python?

Question

I'm trying to calculate geometry in Python for a script tool for ArcMap.

For the script I want to calculate area in hectares. I am trying to use the add geometry attribute (data management) tool, but it's not working and it's giving me all zeros in my output field. This is what I have:

# Set Calculate geometry variables

calculate_table = clip_output

geometry_prop = "AREA"

expression = "HECTARES"

# Run calculate geometry

arcpy.AddGeometryAttributes_management(calculate_table, geometry_prop, "", expression, "")

What's wrong? Should I use a different tool?

Answer 1

try using keyword arguments for the optional arguments in your call to AddGeometryAttributes:

arcpy.AddGeometryAttributes_management(calculate_table, geometry_prop, Area_Unit=expression)

Also, I'm not sure if this is version-specific, but I had to use "AREA_GEODESIC" as the Geometry_Properties, or else I got an error.

edit to answer the second part of your question:

You can use a search cursor to select the records you're interested in with an SQL query, then add up all the areas into a sum variable, then print it using addMessage. It would look something like this:

with arcpy.da.SearchCursor(clip_output, ['area_field'], 'soil_class in (1, 2)') as cur:
  sum = 0
  for row in cur:
    sum += row[0]

arcpy.AddMessage(sum)