Setting up Concatenation using Python expression in field calculator?

Question

I am having trouble creating a Python expression in Field Calculator in ArcMap 10.3.1. I’m attempting to concatenate two field values (double and short integer) to a third (double) field, (CON_IN). I need to allow only two digits to be added to the system number, so if the ET_NO value is greater than or equal to 10, do not add “0”. If the ET_NO is less than or equal to 9, add “0” and the value.

The final output should look like this: 2161400187509 or 2161400187528

I’ve tried variations of this script but get basically the same results. The resulting error shows a syntax error and that SYS_NO is not defined.

Does anyone have any advice?

Pre-logic Script Code:

def   Concat(x,y):

  x= SYS_NO

  y= IN_ETNO

  if y >= 10:

    return x +  y

  elif y<= 9:

    return x +  "0" +  y

Expression:

CON_IN =  Concat( !SYS_NO! , !IN_ETNO! )

---

I see I didn't need to define the x,y. I see by the other posts that I am trying to concatenate a number and a string value, but when I remove the quotation marks on the string it just sums the SYS_NO and ET_NO values which is not what I need. I am not adding the values together, I am trying to add a two digit code to the end of a system number based on unique values for each record.

Answer 1

If you start with a double and want to end with a double, why bother switching to string and back again? Move your SYS_NO over two places by multiplying by 100, then add the IN_ETNO value.

(!SYS_NO! * 100) + !IN_ETNO!

Note that if you're using shapefiles, you may not be able to store the final digit, while GDB feature classes will.

Answer 2

Your error is likely due to the fact that you're trying to concatenate numeric values with a string. You'll need to convert the other values before trying to concatenate with a '0'. Having said that, it seems like you're simply trying to pad the 'y' value with a single '0'. If this is correct, then you can actually use the zfill function to pad the final digit up to a total length of 2.

#if x value is a double, you'll need to remove the decimal def concat(x,y): return str(x).replace('.','') + str(y).zfill(2)

Answer 3

This can be simplified quite a bit with string.format(), which can be configured to zero-pad your values. You don't need a code block at all, actually:

"{f1}{f2:02d}".format(f1=!CON_IN!,f2=!ET_NO!)


>>> "{f1}{f2:02d}".format(f1=21614001875,f2=9)
'2161400187509'
>>> "{f1}{f2:02d}".format(f1=21614001875,f2=28)
'2161400187528'

Answer 4

The reason you're getting the message SYS_NO is not defined is because you have already set x = !SYS_NO! by passing CON_IN = Concat( !SYS_NO! , !IN_ETNO! ).
In def Concat(x,y): you've specified that the first parameter is x and the second is y, so passing !SYS_NO! as your first parameter means that you're setting x = !SYS_NO! there.

def   Concat(x,y):
    xx = int(x)
    yy = int(y)    
    if yy >= 10:
        return '{}{}'.format(xx, yy)
    elif yy<= 9:
        return '{}0{}'.format(xx, yy)

Expression:

CON_IN =  Concat( !SYS_NO! , !IN_ETNO! )