Chapter 32. Exception Basics

This part of the book deals with exceptions, which are events that can modify the flow of control through a program. In Python, exceptions are triggered automatically on errors, and they can be triggered and intercepted by your code. They are processed by four statements we’ll study in this part, the first of which has two variations (listed separately here) and the last of which was an optional extension until Python 2.6 and 3.0:

try/except

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Catch and recover from exceptions raised by Python, or by you.

try/finally

Perform cleanup actions, whether exceptions occur or not.

raise

Trigger an exception manually in your code.

assert

Conditionally trigger an exception in your code.

with/as

Implement context managers in Python 2.6 and 3.0 (optional in 2.5).

This topic was saved until nearly the end of the book because you need to know about classes to code exceptions of your own. With a few exceptions (pun intended), though, you’ll find that exception handling is simple in Python because it’s integrated into the language itself as another high-level tool.