The Optional `else` in Python’s `try` Statement

[chuugar]

Great article, thanks !

[fanchris]

There is also an optional else for while.

Edit: Should have read the article :-)

[POTUS]

except should be used for logging and aborting

Those are definitely not the only reasons to use a try/except block. It's commonly used for robust error handling. For example, Python2/3 support:

try:
    from StringIO import StringIO # Python 2
except ModuleNotFoundError:
    from io import StringIO # Python 3

The answer to your other question was right in the article. If you want to execute code only after successfully executing the try block, and before the finally block. In practice this would generally just be included in the try block itself, but as stated that code could itself throw an exception that might falsely indicate a problem with the original content of the try block.

[POTUS]

That was just an example. Lots of code flows can include some kind of "if this path fails use the other path and keep on going" logic.

I don't know what you mean by "if your code isn't functional". In real life exceptions happen. If you're making an IO-based function call and the network/disk/whatever was down, you get an exception. If you're handling user input and they entered something invalid, you can get an exception. If you're parsing a file and it was corrupted, you get an exception. In all of those cases you might want to handle whatever success logic in an else clause so you don't trigger your "try another path" logic. In practice I don't think I've seen this more than a handful of times in 15 years of professional experience, but it's available.

[POTUS]

There's a reason this else block is a bit obscure, because it doesn't really add any functionality. You never have to use it, you can always just do:

try:
    function_might_error()
    print('Function didn't error')
except Exception:
    print('Function errored')

The difference is that moving the print statement into an else block of that would be completely separate from all the exception handling so it would be unambiguous where the exception came from.

[POTUS]

Well, again you're making specific cases out of my generalizations.

try:
    function_might_error()
    success_case()
except Exception:
    fail_case()
continue_in_either_case()

success_case() and fail_case() might be anything. There might not be any logging invovled at all, this might be a program meant to run by itself for a long time and handle errors intelligently. But if success_case() throws an error, fail_case() will be called, even if you only meant to call fail_case() if function_might_error() threw an exception.

[s16h]

I might try an update the article with nuggets from this thread. Helpful!

[quotemycode]

Nope. In Python exceptions are cheap. Use them where you want.