this post was submitted on 12 May 2024
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Meme is funny, but that exception used as flow control hurts.
Tbf python guidelines encourage it over if/else in cases like this. "Easier to ask for forgiveness than for permission" or something along the lines
pythonic != good
Truers, just mentioning it
Day 598 of asking for a way to tell which functions throw exceptions in Python so I can know when to wrap in try catch. Seems to me that every other language has this, but when I've asked for at least a linter that can tell me I'm calling a function that throws, the general answer has been "why would you want that?"
How am I supposed to ask for forgiveness if it's impossible to know that I'm doing something risky in the first place?
Yeah, for this reason I would pretty much never encourage exceptions in Python over some other form of error handling. It's so frustrating when called code throws some random exceptions that are completely undocumented. This is one of the few things Java got (sort of) right
I believe raises is the de facto Python version of
throws, but no tools seem to exist to actually handle it.that's still a docstring, idk of linters that take docstrings into account at all. We need a semantic approach for this kind of annotation.
That's way harder to ask for. A docstring solution is fine so long as the linters know to pick it up.
I don't think so. A half-measure using docstrings would likely take more processing power and require an ad-hoc implementation because comments are not broken down into ast components afaik. It would also be more costly in the long run if they decide to convert it into a proper syntax, as a result of docstrings not having a single standard way of being written.
Python has introduced several syntactic changes for type annotations, this is not unreasonable.
cant practically anything throw an exception given the right (sometimes extremely remotely possible) circumstances?
Not really. Exceptions are a controlled way of indicating something went wrong in an application.
The only point where you wouldn't know about the possibility of one is when you don't know enough about the language features you're using or when you use a badly documented library or framework.
dont many of the language primitives confer the possibility of thrown exceptions?
Is this feature common in scripting/interpreted languages? Feels like those two things don't work together.
Well at least php has it, which is a JITed scripting language just like Python. Although saying php has it is wrong, it's just a special doc tag that the linters pick up. Which is exactly what I want for Python. The only other scripting language I'm very comfortable with is typescript, which can also support
@throwsvia jsdoc and eslint.So to answer your question, I don't know if it's common, but from my minimal sample pool it's at least not unheard of.
You may not know this (just guessing because you commented on the nature of scripting/interpreted languages) but static analysis of dynamic languages has come really far and is an indispensable part of any reasonably sized project written in them these days. That's another reason why I'm so surprised and frustrated by the lack of this in Python.
Check out Rust
Respectfully, no. Rust is great for some things and Python is great for other things. Switching to rust is not a solution to missing exception linting in another language.
Check it out anyways
Do you have a specific PEP you're referencing or is this one of those "I assume this must be the case because of how common using try/except statements for flow control are" kind of things?
Pretty sure its not a PEP, but the python glossary mentions it. Searching 'python EAFP' brings up a lot of discussion on the topic too, so if nothing else its definitely a widespread phenomenon
I think there's a difference between "python guidelines encourage" something and "this is a common coding pattern." Yes, you can use try/except for flow control, but there's a lot of people, myself included, who try to use that style sparingly.
Like most things in life, context matters. In the OP it seems like the
checkfunction is used specifically so it could raise aPaymentExceptionif the payment hasn't been received... That's not a "forgiveness/permission" context, this is a yes or no question, hence should have been an if.Still hurts, but sometimes it's the only option.
If you're trying to confirm things like account existence/deletion, there's often no "account exists" function to return true or false. You just have to figure out the specific exception thrown and catch that specific one.
The worst are libraries that don't give specific exceptions, so you have to catch all exceptions then do extra work to tell what the specific situation is. Does the account not exist, or is the system unreachable?
Yeah, I had a similar case with some authentication middleware I used that was part of a library.
It would always throw an exception when a user wasn't authenticated instead of just giving me some flag I could check.
Wouldn't have done it that way, but it was okay for an API controller.
That’s horrifying. That’s a solid reason to avoid Python like the plague.
While i also disagree with python's tendency to use exceptions as control flow
Python is a pretty stellar scripting language. I wouldn't use it for app dev, but it's quite handy for the odd automation or CLI task
I've done a little bit of Python in the past, the biggest thing being an automation task that borderline became an app. I certainly can imagine using it for scripts, though I default to bash because that's almost always available but TBH mostly because inertia. Beyond that my default is Go because inertia (and I love Go). I watched a video by the Primeagen (on YT) - in his view, Rust is better for text/data pipelines and CLI tools. Being very familiar with Go and not at all familiar with Rust, that's an interesting take because honestly writing a CLI in Go is kind of meh.
nothing wrong with that - it is an exception, as in, the customer is likely lost after that anyway.