Conditionally labeling layer based on three fields

Question

I am labeling our power line span layer based on the conductor/wire type.

This information is located across three fields in the span layer which represent phases A,B,C.

Basically I want code that will:

Display conductor_a, 

if conductor_a is blank display conductor_b, 

if conductor_b is blank display conductor_c

I am unsure if python or VB would be better for this. Unfortunately I am having difficulty with entering python into the provided window. I've managed to make the following VB code

[gs_conductor_a] & vbCrLf & [gs_conductor_b] & vbCrLf &  [gs_conductor_c] 

This displays the conductor name, but might display up to three labels, which creates a large visual mess in some instances. I want to create a labeling system where there is only one label displayed per line segment. It is worth noting if more than one phase is populated the conductor is the same for all populated fields so anyone of the three will do, but it needs to display only one label total.

Answer 1

I'm not familiar with VB, but the following Python may do what you're after (with the 'Advanced' checkbox ON, and assuming a Shapefile where NULLs are not possible):

def FindLabel ( [conductor_a], [conductor_b], [conductor_c] ):
    if len([conductor_a]):
        return [conductor_a]
    elif len([conductor_b]):
        return [conductor_b]
    else:
        return [conductor_c]

If your feature class is in a geodatabase and not a Shapefile (so that it can contain NULLs and not just blanks), you can check for both NULLs and/or blanks instead of just checking for blanks (zero-length strings):

def FindLabel ( [conductor_a], [conductor_b], [conductor_c] ):
    if [conductor_a]:
        return [conductor_a]
    elif [conductor_b]:
        return [conductor_b]
    elif [conductor_c]:
        return [conductor_c]
    else:
        return ""

Answer 2

This may work as well:

def FindLabel ( [conductor_a], [conductor_b], [conductor_c] ):
    return [conductor_a] or [conductor_b] or [conductor_c] or "ANY VALUE IF ALL PRIOR FIELDS ARE EMPTY"