Fix If/Else Loop with UpdateCursor when attribute value is Null

Question

I have a python script that I use to make batch updates on a database in GIS.

I'm using Update Cursors to update the values of an attribute table, which has worked flawlessly when I am updating records for the first time since UpdateCurosrs overwrite the data (from what I understand as a still-newish coder).

When I revisit a record and need to add (or append) comments to a populated record, I can do so in two different chunks of code, but its clunky and requires additional steps. I'm trying to combine these two pieces of code into a single script with a nested if/else loop.

To overwrite blank attributes, this code works perfectly

fc=DB
fieldname=["StationID","StationStatus","StatusComments_Source"]

for i in confirm: 
    with arcpy.da.UpdateCursor(fc,fieldname) as cursor:
        for row in cursor:
            if (row[0]== i):
                row[1]= "Confirm" #Data Confirmed
                row[2]= StatusComments_Source #Comments    
            cursor.updateRow(row)

If I want to append comments to existing fields, this code works perfectly. This code will break if that attribute field for row2 is empty.

for i in confirm: 
    with arcpy.da.UpdateCursor(fc,fieldname) as cursor:
        for row in cursor:
            if (row[0]== i):
                row[1]= "Confirm" #Data Confirmed
                confcom=[]
                confcom.append(StatusComments_Source)
                row[2]=''.join(confcom)
            cursor.updateRow(row)

This is the loop I tried to create, "If row2 is null, overwrite the data, else: append the comments

for i in confirm: 
    with arcpy.da.UpdateCursor(fc,fieldname) as cursor:
        for row in cursor:
            if (row[0]== i):
                row[1]= "Confirm" #Data Confirmed
                if row[2] is None:
                    row[2] = StatusComments_Source
                else:
                    confcom=[]
                    confcom.append(row[2],", ")
                    confcom.append(StatusComments_Source)
                    row[2]=''.join(confcom)
            cursor.updateRow(row)

But I get this error:

Traceback (most recent call last):

  File "C:\Users\CEI2\AppData\Local\Temp\ipykernel_19768\350652596.py", line 13, in <cell line: 4>
    confcom.append(row[2],", ")

TypeError: list.append() takes exactly one argument (2 given)

I'd appreciate any help with this!!

Answer 1

If you have an existing comma-separated field, and you want to add another item to it, use split() to separate it into a list, append to that list, join it back to a string and assign that back to the field.

if row[2] is None:
    row[2] = StatusComments_Source
else:
    confcom=row[2].split(', ')
    confcom.append(StatusComments_Source)
    row[2]=', '.join(confcom)

You can also just use string concatenation:

row[2] += f', {StatusComments_Source}'