Can ArcGIS geoprocessing tools be used in ArcGIS Field calculator?

Question

Can you put ArcGIS geoprocessing tools such as arcpy.SelectLayerByLocation_management() or arcpy.MakeFeatureLayer_management() into the code block of the ArcGIS Field-calculator (ArcGIS Desktop 10.4)?

Answer 1

Yes, this can be done with some of the geoprocessing tools.

Proof of concept - use arcpy.GetCount_management() to count the selected features and write that value to those selected features:

def myTest():
    count = int(arcpy.GetCount_management('testPoint').getOutput(0))
    return count

Another, use arcpy.SelectLayerByAttribute_management() to select every ObjectID divisible by 4 and write a value to those newly selected features:

arcpy.SelectLayerByAttribute_management('testPoint','NEW_SELECTION','mod(OBJECTID,4)=0')
def myTest():
    return 123

Of course you can make these more complex if you require, however I would recommend using arcpy script tools and update cursors if you're getting too clever, rather than Field Calculator.

Answer 2

I generated random points inside 4 polygons shapefile, using field "Points_Cnt". The source of polygons is "C:\FELIX_DATA\SCRARCH\fish_net.shp":

The result of this field caluclator expression on a new field "RESULT":

mxd = arcpy.mapping.MapDocument("CURRENT")
LR=arcpy.mapping.ListLayers(mxd)[0]
d=arcpy.Describe(LR)
def getPoints(fid):
 arcpy.MakeFeatureLayer_management ("C:/FELIX_DATA/SCRARCH/fish_net.shp","A",'"FID" ='+str(fid))
 arcpy.SelectLayerByLocation_management(LR,"INTERSECT","A")
 nSel=len(d.FIDset.split(';'))
 return nSel

--------------------

getPoints( !FID!)

Confirms that it is possible to use tools in field calculator.