Splitting ID number along hyphens and creating new field with only parts of ID In Field Calculator?

Question

I have a shapefile with polygons and each polygon has an ID number that follows a pattern like this:

SMP_ID
1077-1-1
8-2-2
1281-1-3
304-2-1

In have created a new field and I need to populate it with a truncated version of these IDs, which would look like this:

SYS_ID
1077-1
8-2
1281-1
304-2

This is the code I've been fiddling with most recently, I feel like it's the closest...

def getSysID(SMP_ID):
 if SMP_ID is None:
  return None
 else:
  SysID = SMP_ID.split('-')[0] + '-' + SMP_ID.split('-')[1]
  return SysID

I also tried this method:

id_vals = !SMP_ID!.split("-")

SYS_ID = id_vals[0] + "-" + id_vals[1]

remainder = id_vals[2]

Something isn't working right, though! There are a few IDs from a different source that don't follow this pattern and are just a string of numbers without hyphens, I'm wondering if that could be a part of the problem?

I'm looking for a solution that will ignore the non-hyphenated IDs and nulls, and copy the truncated hyphenated IDs into a new field.

Answer 1

Using the built-in string method of 'find', you can identify whether there is a hyphen in the field and process accordingly. One reason you may have errors is that on non-hyphenated records, there is no item at index position 1 from the split.

def getSysID(SMP_ID):
   if SMP_ID.find("-") == -1 or SMP_ID is None: #might be able to leave off the or clause here
       return None
   else:
       SysID = SMP_ID.split('-')[0] + '-' + SMP_ID.split('-')[1]
       return SysID