Error 999999 when using .isalnum in ArcGIS field calculator?

Question

ArcGIS keeps throwing an error when I use the following script in the field calculator, using Python:

pre-logic script code:

y= ()
if !fieldx!.isalnum():
    y= 1
else:
    y= 0

Fieldy=

y

The error in the results window reads:

'ERROR 999999: Error executing function, Syntax Error, Failed to execture (CalculateField)'

I've checked the classes of the fields: fieldx is a string and fieldy a short integer, so that can't be the problem. I've also enabled the shapefile for editing. Note that I've added fieldy using the addfield function.

Other fieldcalculations, for example:

fieldy = 5

do work, so the problem should be in the syntax.

What am I doing wrong?

Answer 1

That needs to be treated as a function.

In your code block:

def AlnumField(field_value):
   if str(field_value).isalnum():
     return 1
   else:
     return 0

Then in your expression: AlnumField(!fieldx!)

The !fieldname! notation is only respected in the expression, not the code block.