Obtain attribute value from a specific field

Question

I have a point shapefile with a high number of attribute fields. For a single point, there is only 1 of these attribute fields completed, the others have a "NULL" value for that point. The field name for which a value is available is furthermore defined in the field "Blockname".

So, for point 1, the value in the field "Blockname" is OVSTNP_180. In the field "OVSTNP_180" (and only in this field), there is a value listed (e.g. 741).

In order to label the points, I would like to create a field "label" where this value (741 in the example above) is calculated. Which expression do I need to use (in ArcGIS)?

I assumed that, for example in ArcGIS, I could state something like this: Label= ["[Blockname]"] but that does not work...

Answer 1

Since all other fields are <Null>, the following works, although it probably won't be very performant if you have lots of points and fields. I'd suggest using the same logic in field calculator to populate your label field.

Note, I'm not using field at all.

def FindLabel ( [a] , [b] , [c] ):
  return max([a] , [b] , [c])

If say, the other fields weren't all empty, the following would work to populate your label field properly based on the value in field.

fc = '/path/to/fc'
fields = ['a', 'b', 'c']
source = 'field'
label = 'label'

with arcpy.da.UpdateCursor(fc, [source] + fields + [label]) as uCursor:
    for row in uCursor:
        row = list(row)
        i = fields.index(row[0]) + 1   # adding 1 since source is first
        row[-1] = row[i]
        uCursor.updateRow(row)