Adding current row in arcpy.SearchCursor to selection

Question

I want to make a code that select all unique values of a field in a attribute table. However, while everything in the code apparently works, I don't know how to add the current row in the Search Cursor in my selection.

 layer = parameters[0].valueAsText
 mylist = []
 rows = arcpy.SearchCursor(layer, fields="Surveyor")
 for row in rows:
 value = row.getValue("Surveyor")
 if value not in mylist:
 mylist.append(value)
 arcpy.SelectLayerByAttribute_management(layer, 'ADD_TO_SELECTION')
 arcpy.AddMessage(mylist)
 return

On the message (second last line), the program prints a list with 3 unique values. Yet, the code always select every single row. Makes sense, since there was no filter on my SelectLayer, so it just select the whole layer. So I tried using a field with Unique Values:

 layer = parameters[0].valueAsText
 mylist = []
 rows = arcpy.SearchCursor(layer, fields="Surveyor, uniqueID")
 for row in rows:
 value = row.getValue("Surveyor")
 myid = row.getValue("uniqueID")
 if value not in mylist:
 mylist.append(value)
 arcpy.SelectLayerByAttribute_management(layer, 'ADD_TO_SELECTION', '"uniqueID" = myid')
 arcpy.AddMessage(mylist)
 return

But no success, it still selects the whole layer. So, how I make the SelectLayerbyAttribute to add to the selection only the row that the cursor is located?

• Vince: First rule of arcpy.SearchCursor: Use arcpy.da.SearchCursor instead.

Answer 1

"Old-style" search cursors are an artifact of the past. All supported versions of ArcGIS Desktop and Server offer Data Access cursors, which are faster and more Pythonic (list-oriented).

This is one way to rewrite your code, though there are options for faster runtime execution if you know that the number of IDs to be added is a relatively small set (e.g., less than 100-200).

The original problem was not placing the 'myid' value in the query expression.

layer = parameters[0].valueAsText
mylist = []
with arcpy.da.SearchCursor(layer, ['surveyor', 'uniqueID']) as cursor:
 for row in cursor:
 value = row[0]
 myid = row[1]
 if value not in mylist:
 mylist.append(value)
 filterexp = '"uniqueID" = {:d}'.format(myid)
 arcpy.SelectLayerByAttribute_management(layer, 'ADD_TO_SELECTION', filterexp)
arcpy.AddMessage(mylist)
return

Answer 2

Found a solution:

layer = parameters[0].valueAsText
mylist = []
rows = arcpy.SearchCursor(layer, fields="surveyor, uniqueID")
for row in rows:
 value = row.getValue("surveyor")
 myid = row.getValue("uniqueID")
 filterexp = '"uniqueID" = ' + str(myid)
 if value not in mylist:
 mylist.append(value)
 arcpy.SelectLayerByAttribute_management(layer, 'ADD_TO_SELECTION', filterexp)
arcpy.AddMessage(mylist)
return