Calculating a field in modelbuilder

Question

I am trying to update attributes in a table using Calculate Field in Model Builder. I have used the following bit of code but its not updating the field.

    expression:
    Change(!Zone!)

    def Change(Zone):
      if (Zone == "NULL"):
      return "Non UK"

Answer 1

You need to indent the last line as such:

expression:
Change(!Zone!)

def Change(Zone):
  if (Zone == "NULL"):
    return "Non UK"

BUT what if Zone is not null? I assume you want to return it's value? Thus the code should be:

expression:
Change(!Zone!)

def Change(Zone):
  if (Zone == "NULL"):
    return "Non UK"
  else:
    return Zone

Answer 2

Try this

    def Change(Zone):
        if not(Zone):
           return "Non UK"