This operation is using the Field Calculator in ArcGIS Pro 2.1.

I am trying to calculate the Polsby-Popper Score for Congressional Districts. I have calculated the Geodesic Area and Geodesic Perimeter for each feature using this formula:

(12.56637 * !AREA_GEO!) / (!PERIM_GEO! ^ 2)

It is returning the error:

ERROR 000539: Traceback (most recent call last): File "", line 1, in TypeError: unsupported operand type(s) for ^: 'float' and 'int'

I am not sure what exactly this error means.

  • what type of field are you making the calculations (e.g. float, integer, text, etc.)?
    – Aaron
    Commented Feb 20, 2018 at 3:19
  • you want to square !PERIM_GEO!, is that correct? It doesn't like the mixed type, try !PERIM_GEO! * !PERIM_GEO! instead. The value '2' is an integer but !PERIM_GEO! is a float type hence the error message; this operator doesn't do what you think it does in python, it's a bitwise XOR, not an exponent (like C). Commented Feb 20, 2018 at 3:19
  • We have a self-assembling FAQ on ERROR 000539.
    – PolyGeo
    Commented Feb 20, 2018 at 4:08

1 Answer 1


As was mentioned in the comments, your formula should read:

(12.56637 * !AREA_GEO!) / (!PERIM_GEO! ** 2)


(12.56637 * !AREA_GEO!) / (!PERIM_GEO! * !PERIM_GEO!)

This page on python operators shows that the ^ operator is Bitwise XOR.

  • That worked. Both of the input fields are Doubles and the output field is a float.
    – SteveC
    Commented Feb 20, 2018 at 3:32

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