Python Search cursor: Error handling

Question

I have a search cursor that using a SQL query to match addresses and then returns the associated roll number with that address. However, some addresses do not match the roll number and then I believe the search cursor stops. Is there a bit of code I can throw in that will continue with the next address even if a match isn't found? I think an 'if' statement would work well, but I don't know what to write for it!

I'm having trouble generating this. My code is iterating through foldernames to get the address and querying a parcel layer.

I can post the code later, if you need an example.

import arcpy
import os
import re
import sys
import traceback
import collections
basedir = r"C:\Test"
fc = r"G:\ParcelsFixNames.shp"
field1 = "ADD1"
field2 = "STREETNAME"
try:
#find all foldernames in directory
 for fn in os.listdir(basedir):
 string = str(fn)
#split name at hyphen 
 if re.findall('-', fn):
#right side of hyphen is street address, leftside is street name
 lhs, rhs = string.split('-')
 street = str.lstrip(lhs)
 street = str.replace(street,'.','')
 street = str.rstrip(street)
 street = str.upper(street)
 add = str.lstrip(rhs)
 expression3 = '"{field1}" = \'{add}\' AND "{field2}" LIKE \'%{street}%\''.format(field1=field1, add=add, field2=field2, street=street)
 rows = arcpy.SearchCursor(fc, fields="STREETNAME; ARN; ADD1", where_clause=expression3)
 for row in rows:
 Roll = row.getValue("ARN")
 newname = str(Roll)
 newpath = os.path.join(basedir, newname)
 #if the name exists already add _1 to end
 if os.path.exists(newpath):
 os.rename(os.path.join(basedir, fn),
 os.path.join(basedir, newname + "_" + "1"))
 else:
 os.rename(os.path.join(basedir, fn),
 os.path.join(basedir, newname))
 else:
 print add + " " + street + " " + "Already exists...passing"
 continue
except:
 print ("Error occurred")
 tb = sys.exc_info()[2]
 tbinfo = traceback.format_tb(tb)[0]
 pymsg = "PYTHON ERRORS:\nTraceback Info:\n" + tbinfo + "\nError Info:\n " + \
 str(sys.exc_type)+ ": " + str(sys.exc_value) + "\n"
 msgs = "GP ERRORS:\n" + arcpy.GetMessages(2 )+ "\n"
 print (pymsg)
 print (msgs)

• Jason Bellino: Posting the code you are working with is always helpful to get things started.
• GISHuman: @Jason added... it's involved...
• Jason Bellino: Which bit of the code is the one that fails when a match is not found? I'm a little confused as to what you mean by the address not matching the roll number...I assume you are comparing the roll number associated with an address in your feature to another roll number value taken from somewhere else?
• Paul: If there are no features returned by a search cursor, it should pass right over your for row in rows. What version of ArcMap are you using?
• GISHuman: @Paul 10.1 I'm running this as a standalone script in pyscripter

Answer 1

Since you are using Arc 10.1, use the data access module to create your search cursors. As @Paul mentions, they are much better at releasing file locks, especially when using with/as:

fields = ["STREETNAME", "ARN", "ADD1"]
with arcpy.da.SearchCursor(mySitesTbl,fields,where) as rows:
 try:
 if rows.next() != ():
 rows.reset()
 for row in rows:
 ...
 except StopIteration:
 print('Empty Cursor')

• Paul: Your syntax on fields should read ["STREETNAME", "ARN", "ADD1"]. You also cannot access the length of a cursor object.
• Jason Bellino: So instead of using len(rows) > 0, try testing the search cursor for the empty tuple: if rows.next() != (): or something similar.
• Jason Bellino: @Paul is correct, the search cursor object has no variable length. I have updated my answer to focus on using the data access module of Arc 10.1 and a better way to test for an empty cursor.
• Paul: +1 Yep, that works. If OP wanted to pass over it instead of stopping (which I think he wants), it's a simple change to pass. Still, I've never had an issue with an empty cursor stopping my code.
• GISHuman: Upon further inverstigation I think an issue lies with the existing folder names, some contain suffixes such as "ST, DR, AVE, CRT" etc which do not match the street name's in the database... now I just gotta figure out how to remove the suffixes!

Answer 2

maybe try a different cursor..

#arcpy.da.searchcursor is faster
f1, f2, f3 = "STREETNAME", "ARN", "ADD1"
x= 0
with arcpy.da.SearchCursor(fc, (f1, f2, f3), where_clause=expression3) as scur:
 for row in scur:
 x=x+len(row)
 #if you're really curious about how many matches meet the expression3 you could
 #do this - there's probably a more elegant way though!
 print x
 if x > 0:
 with arcpy.da.SearchCursor(fc, (f1, f2, f3), where_clause=expression3) as scur:
 for row in scur:
 .... 
 else: 

• mwil: sorry... i don't know how to post so the code looks right and hashes stay in. oh. and now i see Jason's answer
• Paul: Instead of using three variables, you could just set f1 to a list. See my comment on Jason's answer.
• mwil: @Paul are you sure? the output of arcpy.da.searchcursor is a tuple.. so we should be able to len() it.. i can't test at the moment
• Jason Bellino: It's actually the rows.next() method of the search cursor which returns a tuple
• Paul: @megwilliams, I'm sure. I'm looking at the results right now. TypeError: object of type 'da.SearchCursor' has no len()