Create selection from Python list

TomGeo — Fri, 16 Apr 2010 07:30:48 GMT

Dear all,

I was wondering if it is possible to create a query for a selection from a Python list.
The Python list is created from features in a FeatureClass but since the geoprocessor is very slow I write all the features into a Python list and do all the analysis with Python lists for better performance.
While the performance of getting all the features of interest is good, I do not know how to select all the features in the actual FeatureClass based on my resulting list.

If someone has an example for?

Thanks in advance, Thomas

Create selection from Python list

RDHarles — Sat, 11 Dec 2021 20:41:16 GMT

I can't tell exactly what you are trying to do, but here's an example of using items in a list for selections using a query.

myList = ["apple","pear","orange"]
for item in myList:

    # Select item in list based on field COUNTRY.
    qry = "\"COUNTRY\" = '"+item+"'"

    gp.Select_analysis(inFile, outDir, qry)

Creating queries with keys

KimOllivier — Sat, 11 Dec 2021 20:41:18 GMT

Yes, this is a very successful way of creating an SQL query that is efficient.
A keyfile type selection is often wanted, and the MakeQueryTable is buggy at 9.3 and has a lot of limitations.
You have to have all features in the same geodatabase, complex expressions are not supported in file geodatabase and so on.

Here is my workaround:
Loop through the first table with a cursor to collect a list of keys.
Pass it through a SET structure to remove duplicates.
Create a (potentially huge) sql expression
Use this expression on the source featureclass to create a layer
Process or export the layer to a new featureclass

# to make a keyfile
# 26 April 2010 kimo
# much better than MakeQueryTable and it works across geodatabases
# still uses an SQL query but python generates the set for the expression
# will work for tens of thousands of keys (amazing)
# if you want to save the featureclass or table as a layer or view definition
# to use in ArcMap (without making a copy) you MUST have an index on the key field
# or it will be extremely slow to draw.
# see the Keyfile tool in ArcScripts for an alternative method using selection sets in ArcMap

import arcgisscripting,sys,os,datetime,fileinput
gp = arcgisscripting.create(9.3)

def titlekey(title) :
    gp.Workspace = ws
    # Make a title set to use as a keyfile
    lstTitle = []
    cur = gp.SearchCursor(title)
    row = cur.next()
    while row :
        lstTitle.append(row.ttl_title_no)
        row = cur.next()
    del row,cur
    return set(lstTitle)

def title_tab(src) :
    " use setTitle to export records to a table"
    start = datetime.datetime.now()
    gp.Workspace = ws
    setTitle = titlekey(title)
    expTitle = ",".join(["'"+t+"'" for t in setTitle])
    sqlQuery = "ttl_title_no in ("+expTitle+")"
    gp.MakeTableView_management(src,src+"_view",sqlQuery,wsout)
    gp.OverwriteOutput = True
    gp.CopyRows_management(src+"_view",wsout+"/"+src+"_sub")
    print gp.GetCount(wsout+"/"+src+"_sub").Getoutput(0),"records in "+src+"_sub"
    print datetime.datetime.now() - start
# ------------------------- main -------------------------
title = "e:/arrears.mdb/title"
ws = "e:/memo.gdb"
wsout = "e:/arrears.mdb"
# create subsets based on title keys
if not gp.Exists(wsout+"/tta_sub") :
    title_tab("tta")

topic Create selection from Python list in Geoprocessing Questions

Create selection from Python list

Create selection from Python list

Creating queries with keys