Rounding numbers in a Python Label Expression

Question

I'm having trouble rounding a percentage number using a label expression in Python. Just displaying the label as shown below is fine.

def FindLabel ( [Deaths], [PercentageDead] ):
    if ([Deaths]) == "0":
        return [Deaths]
    else:
        return [Deaths] + "\n" + [PercentageDead] + "%"      

I tried implementing the example given on Arcgis online but as soon as I try to round off the extra digits in my percentage all of those features go blank on my map. No label is displayed whatsoever for those feature.

def FindLabel ( [Deaths], [PercentageDead] ):
    if ([Deaths]) == "0":
        return [Deaths]
    else:
        P = round(float([PercentageDead]), 5)
        return [Deaths] + "\n" + P + "%"      

I've tried converting to a float or an int, and than converting it back to a string but nothing seems to work. If I try to manipulate that field whatsoever the expression will return nothing.

I just want to round off the digits to 5, how would I do that? I'd be willing to switch to Arcade if it would yield the same result.

Answer 1

Your P variable is a number and you're attempting to use the + operator with a number and strings. You cannot do this. You can + two strings or two numbers, but not a string and a number.

There are a few alternatives that you could try. My preference is to use the string format() function to do variable interpolation. It will convert numbers to strings on the fly.

Eg: return "{}\n{}%".format([Deaths], P)

This also has the advantage that it will not fail, even if there is a NULL (None) value, or some other unexpected data type. It will even convert that to a string, so at least you can see where the problem might be.

UPDATE (to address your comment):

The behaviour you've described in your comment is consistent with being unable to convert the string to a float (eg, because it has non-numeric characters in it).

You could wrap this in a try: block to test it, something like:

try:
    pDead = float([PercentageDead])
except:
    return "{}\nFAILED to convert '{}' to float!!!".format([Deaths], [PercentageDead])

P = round(float(pDead), 5)
return "{}\n{}%".format([Deaths], P)