Exceptions: try / except / finally / raise

So far, any runtime error - dividing by zero, looking up a missing dictionary key, indexing past the end of a list - has crashed the whole program. Exceptions are Python's mechanism for handling those errors gracefully: catching them, recovering, or deliberately raising your own when something your code considers invalid happens.

Code that might fail goes inside a `try` block. If an exception occurs, Python immediately jumps to the matching `except` block instead of crashing the program.

You can and should catch the specific exception type you expect, rather than a bare `except:` that swallows everything - including bugs you would actually want to know about, like a `TypeError` from a typo.

A `try` statement can have two more optional clauses: `else`, which runs only if no exception occurred, and `finally`, which always runs, whether an exception happened or not - useful for cleanup that must happen no matter what.

The `raise` statement lets your own code signal that something has gone wrong, using either a built-in exception type or a custom one (covered in the next chapter). Always include a clear message - a future reader (often you, weeks later) will thank you.

• -`try`/`except`: attempt risky code, handle specific failures without crashing.
• -`else`: runs only when the `try` block succeeded with no exception.
• -`finally`: always runs - success, failure, or even a `return` inside the try block.
• -`raise SomeException("message")`: signal your own failure condition, with a message explaining what went wrong.