Concatenating fields with label expressions using Python

Question

I am trying to combine three numeric fields together for a feature's label. I only want to label the feature if it is over 0. The labeled numbers need to be separated a dash ("-"). This is what I attempted to use as the label expression in ArcMap 10.2:

def FindLabel ( [a1], [a2], [a3] ):
    if ([a3]) == 0 and int([a2]) == 0 and ([a1]) == 0:
        label = " "
    elif ([a3]) == 0 and int([a2]) == 0
        label = [a1]
    elif ([a3]) == 0
        label = [a1] + "-" + [a2]
    else:
        label = [a1] + "-" + [a2] + "-" + [a3]
    return label

Answer 1

This function doesn't need to be too complex. Convert the items you want into a list, then join the result.

def FindLabel([A1], [A2], [A3]):
    args = [A1, A2, A3]
    items = [str(x) for x in args if bool(x) and int(x) > 0]
    if any(items):
        return '-'.join(items)
    else:
        return ' '

If this were proper Python, you would normally use *args to accept any number of arguments into a list.

Answer 2

There are missing semi-colons and problems with the parentheses. then you should make sure that you always have a string output.

EDIT : sorry, I've given a solution for the field calculator. This solution is updted for the labelling engin.

def FindLabel ( [A1], [A2], [A3] ):
    a1=[A1]
    a2=[A2]
    a3=[A3]
    if ( (int(a1) == 0) and (int(a2) == 0) and (int(a3) == 0)):
        label = " "
    elif ( (int(a2) == 0) and (int(a3) == 0):
        label = str(a1)
    elif (int(a3) == 0):
        label = a1 + "-" + a2
    else:
        label = a1 + "-" + a2 + "-" + a3
    return label

note that the following test are equivalent

 int(a1) == 0 

and

 a1='0'

for testing if a field is null, you can use

 if not a1: