Calculating field with ArcPy cursor?

Question

I am trying to calculate field with the formula. I tried arcpy.calculate field management but still having difficulty.

(10/10.4*(100*(math.exp(0.000871* !A!)-1+math.exp(0.000537* !B! )-1+math.exp(0.000487* !C! )-1)))

I used the below code.

with arcpy.da.UpdateCursor(fc, (VALUE, A, B, C)) as cursor: for row in cursor: row[0] = (10/10.4*(100*(math.exp(0.000871* !A!)-1+math.exp(0.000537* !B! )-1+math.exp(0.000487* !C! )-1))) cursor.updateRow()

• Son of a Beach: A field cannot do a calculation by itself. Fields do not have a 'calculation' type. Just text, integers, floats, etc. You may want to look into using a database 'view' which can include automatic calculation columns. In ArcGIS, you can use a 'Query Layer' which is essentially a layer based on a spatial view definition. Or you can just create a spatial view and drag it onto ArcMap. I haven't checked, but there may be arcpy equivalents for doing similar things, but you should probably explain further what you are actually trying to achieve.
• Vince: Please use code block formatting on code. All it takes is indenting four spaces or using the {} button in the editor. The result will be legible code (and fewer downsides)
• Vince: And please don't re-ask questions. All you needed to do was make the code edit and vote to reopen.

Answer 1

#You need to reference each Field its Index in your list of Fields.
# what values are in A,B,C? string, integer,double? you may need to cast them
with arcpy.da.UpdateCursor(fc, ['VALUE', 'A', 'B', 'C']) as cursor: 
 for row in cursor:
 calc_a = math.exp(0.000871* row[1])-1
 calc_b = math.exp(0.000871* row[2])-1
 calc_c = math.exp(0.000871* row[3])-1
 row[0] = (10/10.4 * (100* (calc_a + calc_b + calc_c))))
 cursor.updateRow()