Use Python in ArcGIS Field Calculator to return value based on numeric value in any of three other fields

Question

I am trying to calculate a new field in ArcGIS 10.5 Desktop using the field calculator, based on the value in any or all of three other fields in the same table. I have not used Python for a while, and am forgetting how to do this.

In essence, this should calculate if any of three types of a crop are being grown in an area. If at least one has an area greater than 1 hectare, then it should return "1" (if two or three types are present, it should give the same answer). The input fields and criteria:

• Dry season rice > 1 hectare
• Wet season rice > 1 hectare
• Upland rice > 1 hectare
• If any of these are true, then return "1" to new field I have already created, otherwise, new field is 0.

I have tried a few options in Python, but none have worked so far, e.g.:

def calc(Dry_area_1,Wet_area_1,Up_rice_1):
    if Dry_Rice > 1:
        Grow_Rice = 1
    elif Wet_Rice > 1:
        Grow_Rice = 1
    elif Up_Rice > 1:
        Grow_Rice = 1
    else
        return 0

Am I overlooking something very simple at a late hour of the night here?

Answer 1

You are confusing the way you define the function.

Your function needs to reference the variables(fields) called by the function.

Your function calls Dry_area_1, Wet_area_1, Up_rice_1, yet you don't reference any of those in the function.

You also need to return a value, not assign it to a variable. You're trying to assign Grow_Rice, but you need to return a value instead.

I think this is what you're going for:

def calc(Dry_area_1, Wet_area_1, Up_rice_1):
    if Dry_area_1 > 1:
        return 1
    elif Wet_area_1 > 1:
        return 1
    elif Up_rice_1 > 1:
        return 1
    else:
        return 0

then in the expression box:

calc(!Dry_area_1!, !Wet_area_1!, !Up_rice_1!)