This post is a followup to my article The Basics of Exceptions in Python, but should make sense on its own as long as you are familiar with raise and try/except.
Let’s cover a few more advanced aspects of the Python exception system. We’ll move a bit faster and talk at a higher level than we did in the last post.
Topics we’ll hit:
This post was originally meant to be a small part of my discussion of the Go programming language (coming soon) as a way of drawing contrast between Python and Go, but turned out to be extensive enough to justify its own post.
Python’s model of exceptions is quite similar to that of other popular object-oriented languages like Ruby, JavaScript, and Java1. Errors flow differently than regular data; if not “handled”, they rise up through the entire function stack and crash the program. Developers are encouraged to write code to anticipate those exceptions, handle them before everything explodes, and change the logic flow of the program accordingly.
What exactly needs to be done in that “handling” step typically depends on what went wrong, and so there are many types of errors. Programmers can check the type of an error to determine what went wrong and react accordingly. Errors can be thought of as objects and their types as classes that can be subclassed like any other class. But unlike other data, they follow an error-specific path through the code, short-circuitiing functions all the way up the stack until handled.