Chapter Summary

And that is the majority of the exception story; exceptions really are a simple tool.

To summarize, Python exceptions are a high-level control flow device. They may be raised by Python, or by your own programs. In both cases, they may be ignored (to trigger the default error message), or caught by try statements (to be processed by your code). The try statement comes in two logical formats that, as of Python 2.5, can be combined—one that handles exceptions, and one that executes finalization code regardless of whether exceptions occur or not. Python’s raise and assert statements trigger exceptions on demand (both built-ins and new exceptions we define with classes); the with/as statement is an alternative way to ensure that termination actions are carried out for objects that support it.

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In the rest of this part of the book, we’ll fill in some of the details about the statements involved, examine the other sorts of clauses that can appear under a try, and discuss class-based exception objects. The next chapter begins our tour by taking a closer look at the statements we introduced here. Before you turn the page, though, here are a few quiz questions to review.