Error handling with Python script tools

Question

I am trying to integrate some error handling in my python script tools but I am not exactly sure how to do it properly.  The desktop help has a lot of great examples but there are so many different ways of doing this.   I am also a bit confused with the difference between error messaging in standalone script vs script tools??

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//002z0000000q000000.htm

Below is a subset of my script, only showing the error handling portion.
# Import arcpy module
import arcpy
from arcpy import env
from arcpy.sa import *
import sys, string, os
arcpy.env.overwriteOutput = True

try:
    # Check out any necessary licenses
    if arcpy.CheckProduct("ArcInfo") == "Unavailable":
        arcpy.AddError("ArcInfo Licensing Issue")
        raise LicenseError
    if arcpy.CheckExtension("Spatial") == "Available":
        arcpy.CheckOutExtension("Spatial")
    else:
        arcpy.AddError("Spatial Analyst Licensing Issue")
        raise LicenseError

# all all the processing here....

except:
    print arcpy.GetMessages(2)
finally:
    # Check in the Spatial Analyst extension
    arcpy.CheckInExtension("Spatial")

Questions:
-Will the above work properly for script tools?  For the except: block will the print do anything in script tools or do I need to use some other syntax to print the error instead?
-In this particular tool I have a cleanup routine that deletes intermediate files.  I currently have this before the except statement but would like to make sure that if the tool crashes that it cleans-up the intermediate files.  Is it possible to put the cleanup routine within the finally: block?  Is that good coding practice?

Any tips on simple and best practice for error handling in script tools (containing a series of geoprocessing steps) would be greatly appreciated.

Thanks.

Alice

LoganPugh · Answer

I noticed in that the blog uses the "def trace():"  inside (tip#4) or outside (tip#5) the try block?   What is the logic for putting it inside vs. outside?

That's a good question, I hadn't noticed that. I'm not sure, but it looks like a logic error on the author's part. Normally wouldn't want to define a function inside of a try.

AliceDeschamps1 · Answer

I find the traceback functionality very useful and I adapted the scripts examples from the suggested blog link below for ArcGISv10.  I included a snippet of the modified working script.
http://blogs.esri.com/dev/blogs/geoprocessing/archive/2008/12/01/tips-and-tricks-_2d00_-error-handling-in-python-script-tools.aspx

I noticed in that the blog uses the "def trace():"  inside (tip#4) or outside (tip#5) the try block?   What is the logic for putting it inside vs. outside?   
# Import system module
from xml.etree import ElementTree
import arcpy, string, os

def trace():
    import sys, traceback
    tb = sys.exc_info()[2]
    tbinfo = traceback.format_tb(tb)[0] 
    line = tbinfo.split(", ")[1]
    filename = sys.path[0] + os.sep + "test.py"
    synerror = traceback.format_exc().splitlines()[-1]
    return line, filename, synerror

if __name__ == '__main__':

try:
        inShapeFile= arcpy.GetParameterAsText(0) #final edited polygon shapefile
        inFile=arcpy.GetParameterAsText(1) #for R1 is .txt, for R2 is .xml
        polList=str(arcpy.GetParameterAsText(2))#user select from drop list
        
        # all the processing code goes here.....

except arcpy.ExecuteError:
        #Return Geoprocessing tool specific errors
        line, filename, err = trace()
        arcpy.AddError("Geoprocessing error on " + line + " of " + filename + " :")
        for msg in range(0, arcpy.GetMessageCount()):
            if arcpy.GetSeverity(msg) == 2:
                arcpy.AddReturnMessage(msg)
    except:
        #Gets non-tool errors
        line, filename, err = trace()
        arcpy.AddError("Python error on " + line + " of " + filename)
        arcpy.AddError(err)

AliceDeschamps1 · Answer

Thanks for the clarifications and the link.