Running ArcGIS 10.2 here and a complete beginner with Python. I'm trying to figure out a workflow to test for closed polylines using the field calculator. Essentially what I'd like to do is to populate a specific field with "closed" or "open". This is what I've come across and if I understand it correctly, it loops through each row and checks if the first x coordinate matches the last x coordinate, if there is a match then it prints the OID.

How do I convert this to a field calculator expression?

Do I need to use an update cursor rather than search to populate my new field?

fc = "Boundary"  

rows = arcpy.SearchCursor(fc)  
for row in rows:  
    geom = row.shape  
    if geom.firstPoint.X == geom.lastPoint.X:  
        print row.OBJECTID  

del row, row
  • 1
    The answer is Yes. You need to use updatecursor rather than Searchcursor
    – BBG_GIS
    Commented Dec 8, 2017 at 21:02
  • I think you'd better to compare x and y. You are using field calculator. You don't need fc, searchcursor or updatecursor in field calculator
    – BBG_GIS
    Commented Dec 8, 2017 at 21:58
  • Can I do that without creating new fields with the start and end coordinates? @wetland Commented Dec 8, 2017 at 22:04
  • 3
    Possible duplicate of arcpy: get list of adjacent lines per line
    – BBG_GIS
    Commented Dec 8, 2017 at 22:30
  • 2
    Old-style cursors are archaic at this point -- Use DataAccess (arcpy.da) cursors for all your cursor needs.
    – Vince
    Commented Dec 8, 2017 at 22:59

2 Answers 2


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You don't need to use a Cursor. Right-click the Field you want to populate, then enter this info into the Field Calculator.


I modified @klewis answer recently since I was running into an issue where some polylines had null geometry causing the field calculator to error out or give me false positives. Here is the updated code block:

def isClosed(geom):
        if geom.firstPoint.X == geom.lastpoint.X and geom.firstPoint.Y == geom.lastPoint.Y:
            return "1"
            return "0"
        return 'exception'

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