What is the correct or best way to make a python / arcpy script bail out?

[NeilAyres]

You know, the script runs, check various inputs and so forth.

If a requirement is not met, eg the feature is not the correct type or something, then bail out and print a meaningful message.

Currently I use sys.exit(), but this is not ideal and throws an error in python.

So, how do the experts do it?

Thanks in advance,

Neil

[OwenEarley]

The Understanding message types and severity section in the help has some good tips.

Depending on the severity of the issue you can use:

• arcpy.AddError
• arcpy.AddWarning

[BruceHarold]

I always used sys.exit()

[JeffWard]

Read the the "Error Handling" page of the help docs.

[curtvprice]

If this is a python script tool, it's best to take advantage of parameter validation on the inputs -- to filter the input choices and check inputs before the tool is even run. This makes your tool far easier to use.

Help 10.2: Understanding Validation In Script Tools‌

If you want to drop out of your script for some other reason - without generating an error, you can create a custom exception and handle it (as suggested by others above):

class HappyError(Exception):
    pass

try:
    # ...
    raise HappyError("message")
    # ...
except HappyError as msg:
    arcpy.AddMessage(msg)

Proper way to declare custom exceptions in modern Python? - Stack Overflow