topic Re: SelectLayerByAttribute empty selection in Python Questions

SelectLayerByAttribute empty selection

RA1 — Wed, 04 Apr 2012 11:37:51 GMT

How can I use the information from arcpy.SelectLayerByAttribute_management, when I have an empty selection?

If empty:
do something
do somethingelse

Re: SelectLayerByAttribute empty selection

MathewCoyle — Sat, 11 Dec 2021 23:32:37 GMT

You can use getcount to test if there is a selection. You can reverse if you have no selection more often than not, or if you only want to be doing something if there is no selection.

selectcount= int(arcpy.GetCount_management(layer).getOutput(0))
if selectcount != 0:
    do something if a selection
else:
    do something else if no selection

Re: SelectLayerByAttribute empty selection

JamesNunn — Sat, 11 Dec 2021 23:32:40 GMT

I have never been able to make this work as intended; running the script on a layer which has no selection just returns the total number of rows in the feature class. Below is a python function to count the number of rows in a selection using a SearchCursor:

def count_selection(lyr):
    """Returns a count of selected features from an input feature layer."""
    count = 0
    rows = arcpy.SearchCursor(lyr)
    for row in rows:
        count += 1
    return count

Example:

lyr = "Buildings_lyr"

if count_selection(lyr) == 0:
    print lyr, "is empty"

Not as neat as having a working inbuilt function; maybe someone can show me I am using the arcpy function incorrectly.

Re: SelectLayerByAttribute empty selection

ArkadiuszMatoszka — Sat, 11 Dec 2021 23:32:42 GMT

You can use Describe on layer and FIDSet property. It should looks like:

desc = arcpy.Describe(lyr)
if len(desc.FIDSet) > 0: # layer has selection
  doSomething
else:
  doSomethingElse

Cheers
Arek