arcgis.features.FeatureLayer --> calculate

[TomPaschke]

Hi,

I would like to calculate a field value using the 

   calculate(where, calc_expression, sql_format=’standard’)

operation of the arcgis.features.FeatureLayer class.

I have to fields that I want to multiply but

   agg_result.layers[0].calculate(where="1=1",calc_expression={"field": "MIN_value","value" : "!poly_area! *    !MEAN_value!"},sql_format="standard")

is throwing the following error: TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

The CalculateField operation of arcpy is workinf fine:

   arcpy.management.CalculateField(agg_result.layers[0].url, "MAX_value", "!poly_area! * !MEAN_value!",    "PYTHON_9.3", None)

Can anyone tell me what I'm doing wrong?

Thanks!

Thomas