Beginning Python: Exceptions, Errors, and Warnings

If reading the previous page has caused you to wonder: "Gee, what does Python do with unexpected variations in data?", try this in your Python shell:

Python 2.5 (r25:51908, Dec 8 2006, 15:53:50)
[GCC 4.0.3 (Ubuntu 4.0.3-1ubuntu5)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> print a

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'a' is not defined

If you would like another example, try this one from "Beginning Python":

>>> 1/0

If you have come far enough in life to be reading this, there is a good chance that you know that division by zero is a no-no in the world of non-imaginary numbers. Python may not have been around as long as you have, but it knows that, too, and it has a special error just for it:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ZeroDivisionError: integer division or modulo by zero

You will notice that this error is called a ZeroDivisionError. Python has many kinds of exceptions. Descriptions of each can be found on the last page of this tutorial. Alternatively, if you just want to get a feel for what kinds of exceptions can be thrown, type the following in your Python shell:

>>> import exceptions
>>> dir(exceptions)

• What is an Exception?
• Exception Exemplified
• If at First You Don't Succeed
• Try, Try Again
• Taking Exception
• If All Else Fails...
• Raising Your Own Exceptions With raise - Part 1
• Raising Your Own Exceptions With raise - Part 2