Script for updating certain shapefile records meeting different conditions

Question

This is my scenario:

• List of names in a python list: a[]
• A 1000 records shapefile with a column: 'name' (populated)
• A second column called 'value'
• ArcGIS environment (arcpy)

I want to update the column 'value' (i.e from 0 to 1) for all the shapefile records having a value in the column 'name' matching any of the list.

In terms of efficiency, I don't know which one is the best option:

A) Iterate through the list first; for each value of the list I start running through the shapefile asking for a match and do the update. Example: for 3 names; 3,000 reading operations on the shapefile.

B) Iterate through the shapefile first; for each record of the shapefile I look for a match on the list by iterating through the list each time. Example: for 3 names; 1,000 reading operations on the shapefile.

C) Use a dictionary instead, no list. Iterate through the shapefile first, and for each record, ask the dictionary for a value, if any, and do the update. Example: for 3 names; 1,000 reading operations on the shapefile.

Answer 1

If you have your values in a python list already, you only need to iterate through your shapefile. You can check if a value is in a list with if <value> in <list>:.

Example:

#full path to shapefile
shp = "C:\example\exampe.shp"

#check field
nameFld = "name"
#update field
valueFld = "value"
#update value
updateValue = 1

checkList = [...] #your values to check

import arcpy

#iterate rows in table
with arcpy.da.UpdateCursor (shp, [nameFld, valueFld]) as cursor:
    for name, value in cursor:
        #skip row if name value isn't in list
        if not name in checkList:
            continue

        #update
        row = (name, updateValue)
        cursor.updateRow (row)