The simplest way to handle exceptions is with a "try-except" block:
If you wanted to examine the exception from code, you could have:
General Error Catching
Sometimes, you want to catch all errors that could possibly be generated, but usually you don't.In most cases, you want to be as specific as possible (CatchWhatYouCanHandle). In the first example above, if you were using a catch-all exception clause and a user presses Ctrl-C, generating a KeyboardInterrupt, you don't want the program to print "divide by zero".
However, there are some situations where it's best to catch all errors.
For example, suppose you are writing an extension module to a web service. You want the error information to output the output web page, and the server to continue to run, if at all possible. But you have no idea what kind of errors you might have put in your code.
In situations like these, you may want to code something like this:
MoinMoin software is a good example of where general error catching is good. If you write MoinMoin extension macros, and trigger an error, MoinMoin will give you a detailed report of your error and the chain of events leading up to it. Python software needs to be able to catch all errors, and deliver them to the recipient of the web page.
Finding Specific Exception Names
Standard exceptions that can be raised are detailed at:
Look to class documentation to find out what exceptions a given class can raise.
For general (non-Python specific) ideas about exceptions, consult ExceptionPatterns.
To Write About...
- Give example of IOError, and interpreting the IOError code.
- Give example of multiple excepts. Handling multiple excepts in one line.
- Show how to use "else" and "finally".
- Show how to continue with a "raise".
General Error Handling
In the "general error handling" section above, it says to catch all exceptions, you use the following code:
However, it originally was:
Someone pointed out that "except" catches more than just "except Exception, e."
Why is that the case? What is the difference?-- LionKimbro
Getting Useful Information from an Exception
So, I've got something like:
1 (a,b,c) = d
...and Python spits back:
ValueError: unpack list of wrong size
...and so, you naturally wonder, "Well, what was in d?"
You know- you can put a print d in there, and that works. But is there a better, more interesting way to get at that information that people know of?