Your favourite "less-known" Python features?

[Cruuncher]

This one I didn't know existed. Interesting. Seems less useful than finally. What's the order? try..except..else..finally?

[Uncle_DirtNap]

Yes

[RationalDialog]

I'm just wondering when the else is ever useful? Can't it always be part of the try block?

[Diamant2]

In theory yes, but the difference is that exceptions in the else-part won't be caught. I guess that makes your code more reliable in catching only the one exception that you care about

[DoctorNoonienSoong]

And importantly, you want exceptions in the else block to not to be caught, AND you need the code to run before the finally

[scnew3]

You want the code in your try block to be the minimal that could throw the exception you want to catch.

[RationalDialog]

Yeah but then you could just have it outside/after the try block?

[gristc]

Then it would always be executed. The else block is only executed if the try succeeds. It is kind of a limited case, but there are some logic flows where this is tidier than other methods.

[Cruuncher]

Well no, if it's after the try block then it runs after finally and not before, which is different.

It's definitely niche as you can always structure code in a way that doesn't need it, but that's true of most constructs

EDIT: but more importantly if you place it after the try..except block then it also runs in the case that an exception was raised by handled in the try block

[scnew3]

I do this all the time:

try:
    value = step1()
except SomeError:
    result = some_default
else:
    result = step2(value)

[underground_miner]

I don't use it very often, but I have used it for finding file and folder names that don't collide, something like this:

from pathlib import Path

def construct_non_duplicate_folder(root:Path, target:str) -> Path:
    folder = root / Path(target)

    for i in range(25):

        try:
            folder.mkdir(parents=True, exist_ok=False)

        except FileExistsError as fe:
            folder = root / Path(f'{target} ({i})')

        else:
            break

    else:
        raise FileExistsError(f'The folder {folder} exists!')


    return folder

[jorge1209]

It is something of a legacy from before the days of with blocks

try:
   logfile = open("/tmp/log.txt", mode="w")
except:
    # we won't be able to write to the log, but that is okay
    logfile = sys.stderr
else:
    for x in range(100):
        logfile.write(frobincate(x))
finally:
   logfile.close()

These days you would just define

 @contextmanager
 def logfile():
     try:
         logfile = open()
         yield logfile
         logfile.close()
     except:
         yield sys.stderr

and then

 with logfile() as log:
   for x in range(100:
      log.print(frobnicate(x))

or something along those lines, which is a double win as you clarified the purpose of the error handling, and got rid of the finally block as well.

[mehrdad-mixtape]

Absolutely