I am trying to copy the values from one column within my attribute table (!roomName!) over to another column (!spaceDiscriminator!). I understand how to do an easy field calc over for all the values but the problem is, I only want the rows in !roomName! that have values to copy over. If !roomName! contains a Null row then I do not want it copying over, instead I want the original value in !spaceDiscriminator! to remain and not get edited. I cannot figure out how to do this adequately. I have attached my code below:

In the first if statement I have tried many alternative scenarios. If x == None: seems to be the one that accurately selects the Null fields I don't want copying over. return None still edits the !spaceDiscriminator! field however. I've tried to use continue there but it throws and error. Is there any simple statement I can use there that basically says, "if the value is none/Null continue to the next row and leave original !spaceDiscriminator! value".

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2 Answers 2


The code you seek would be something like this:


def testme(x,y):
  if x is None:
    return y
    return x

As you can see you can pass more than one field value into your function, in your case the value from the very field you are updating.

  • Thank you! This seemed to do the trick, much appreciated.
    – DEB
    Commented Aug 31, 2016 at 21:37
  • 1
    @DomB The way to show appreciation for an answer is to upvote it and/or check the green Accept mark next to it. Your rep may prevent you from doing one or both just yet.
    – PolyGeo
    Commented Aug 31, 2016 at 22:06
  • 1
    I would modify the code to test whether x is None as opposed to x==None. See this post.
    – Fezter
    Commented Aug 31, 2016 at 22:17
  • Thank you both. I've also checked the green accept mark as I'm still too low level to upvote. I've updated to is as that works properly.
    – DEB
    Commented Sep 1, 2016 at 19:35

Just Select by Attributes where [RoomName] is not null, then do your simple calculation. Should only operate on selected rows.

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