Passing a variable to Select By Attributes using a 'for' loop in Python

Question

I'm trying to write a script using 'Select by Attribute' in ArcMAP. What I want to do is create a for loop that will pass a value to the Select by Attribute expression. I was thinking something along the lines of: (x=number of polygons in a shapefile)

for j in range(0,x,1):
  arcpy.MakeFeatureLayer_management ("layer", "temp") 
  arcpy.SelectLayerByAttribute_management ("temp","NEW_SELECTION",""" "ID" > j""")
  arcpy.CopyFeatures_management("temp","SlopeG5")

The rest of the scripting I should be able to handle, but when I run this, I get error code 000358, saying that the expression isn't valid. ArcMap doesn't appear to like the 'j' within the select by attributes.

The overall goal is to isolate a polygon, use a select by location to find polygons intersecting, find the area of the two, and divide to get the percentage of the main polygon covered by the second.

Hopefully this description is clear enough to get some help

@interjay I know what it is, but what was your intention with it? — Izkata, Jul 17 '13 at 13:56

score 0 · Answer 1 · answered Jul 17 '13 at 13:57

0

I don't know anything about ArcMap, but you're passing the literal string "j" as a comparison, rather than the value of the variable j. You probably mean:

arcpy.SelectLayerByAttribute_management ("temp","NEW_SELECTION", "ID > %s" % j)

answered Jul 17 '13 at 13:57

Daniel Roseman

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score 0 · Answer 2 · answered Jul 17 '13 at 13:57

It looks like this is what you intended to do - insert the value of j into the string:

for j in range(0,x,1):
  arcpy.MakeFeatureLayer_management ("layer", "temp") 
  arcpy.SelectLayerByAttribute_management ("temp","NEW_SELECTION",'"ID" > %s' % j)
  arcpy.CopyFeatures_management("temp","SlopeG5")

Passing a variable to Select By Attributes using a 'for' loop in Python

2 Answers2