Here is my basic approach to using a dictionary and an update cursor:
import arcpy
target = r'C:\path\to\the\table_to\update'
upDateFields = ['CommonKey', 'FieldN']
source = r'C:\path\to\the\data_that_has\what_target_needs'
sourceFields = ['CommonKey', 'Field1']
sourceDict = {r[0]:(r[1]) for r in arcpy.da.SearchCursor(source,sourceFields)}
with arcpy.da.UpdateCursor(target,updateFields) as updateRows:
for updateRow in updateRows:
keyValue = updateRow[0]
if keyValue in sourceDict :
updateRow[1] = sourceDict[keyValue]
updateRows.updateRow(updateRow)
else:
pass
Having poured through the script for a minute or two, it seems like you are over thinking it a bit. Not a criticism, just an observation. The basic premise is to create a dictionary of the source data using the common key between the source and the target as the key in the dictionary, and then the associated value in that dictionary is what the target gets updated with.
Lets say the common key between the source and the target is a field called FacilityID . Using dictionary comprehension create a the dictionary with a search cursor as shown above and it looks something like this:
{1:'value1',
2:'value2',
3:'value3'}
All you need to do then is look and see if the dictionary key appears in the target, and then used the associated value with that key to update the target field.
A row in a search cursor or update cursor is in the format of a tuple so the first element is row[0].
Make sense?
That should just about do it....
