Python 3.15: features that didn't make the headlines

hckrnws

Python 3.15: features that didn't make the headlines

(blog.changs.co.uk)

424

217

by rbanffy

kokada
782d
From this example:
```
    lazy from typing import Iterator

    def stream_events(...) -> Iterator[str]:
        while True:
            yield blocking_get_event(...)

    events = stream_events(...)

    for event in events:
        consume(event)
```
Do we finally have "lazy imports" in Python? I think I missed this change. Is this also something from Python 3.15 or earlier?
1. llimllib
  232d
  3.15: https://docs.python.org/3.15/whatsnew/3.15.html#whatsnew315-...
  1. javcasas
    222d
    > When an AttributeError on a builtin type has no close match via Levenshtein distance, the error message now checks a static table of common method names from other languages (JavaScript, Java, Ruby, C#) and suggests the Python equivalent
    Oh, that is such a nice thing.
    fulafel
    192d
    It's unrelated to the lazy keyword. Instead it's another feature related to error messages.
    The example:
    >> 'hello'.toUpperCase() Traceback (most recent call last): ... AttributeError: 'str' object has no attribute 'toUpperCase'. Did you mean '.upper'?
2. kzrdude
  72d
  What benefit does the lazy import have here - if we use the value in a type hint at module scope anyway? Would that require Deferred evaluation of annotations -- which I don't think are enabled by default?
  1. js2
    52d
    Type annotations are lazily evaluated by moving them behind a special annotations scope as of 3.14:
    https://peps.python.org/pep-0649/
    https://docs.python.org/3/reference/compound_stmts.html#anno...
    With 3.15, using lazy typing imports is more or less an alternative to putting such imports behind an "if TYPE_CHECKING" guard.
3. karpetrosyan
  32d
  Note that you can work around it by implementing `def __getattr__(name: str) -> object:` at the module level on earlier Python versions
  1. saghm
    02d
    Somehow I have no trouble imagining this being used as a rationale to avoid unnecessary "magic" to the language for years
4. ActorNightly
  02d
  Python has had lazy imports from like day one, where you could have an import statement in a function, and the library won't be imported until that function is hit.
5. Hamuko
  11d
  It's one of the headline features of Python 3.15 (hence why it's not in this article). It's even mentioned as the first thing on the What's New doc, so I'm definitely counting it as a "headline feature".
  Personally, can't wait. It was just this week that I observed a Python process running out of memory because a module import that's not being used during the process was added to the application, and the memory usage went over a critical threshold because of that.
  1. 0cf8612b2e1e
    01d
6. boxed
  02d
  Yes, 3.15+
7. alcazar
  02d
  [dead]
8. rad120
  362d
  [dead]
  1. stingraycharles
    172d
    > Python is such a weird language. Lazy imports are a bandaid for AI code base monstrosities with 1000 imports
    Just because you don’t like a feature doesn’t mean it’s because of AI and bad code.
kwon-young
02d
It's nice that python 3.15 added Iterator synchronization primitives: https://docs.python.org/3.15/library/threading.html#iterator.... These will nicely complement my threaded-generator package which is doing just this but using a thread/process+generator+queue: https://pypi.org/project/threaded-generator/
dhruv3006
01d
> Immutable JSON Objects With the addition of frozendict in 3.15, we now have the ability to represent all the json types (array, boolean, float, null, string, object) in immutable (hashable) forms.
I actually love this last feature !!
JohnKemeny
22d
> I've left this one to the bonus section because I've never used set operations on Counters and I'm finding it extremely hard to think of a use case for xor specifically. But I do appreciate the devs adding it for completeness.
Check out symmetric difference
https://en.wikipedia.org/wiki/Symmetric_difference
1. qsort
  12d
  Yeah, but applied to counters it would be the symmetric difference between multisets, which doesn't have a natural definition. If I understood the proposal they'd be defining it as absolute value of the difference of the counts, which isn't even associative.
  If they only considered parities it could be interpreted as addition in F_2, which is more natural, but I'd still agree that it's hard to see how you'd use something like this in practice.

jwineinger

12d

One of the Counter examples is incorrect, tested on both 3.13 and 3.15.0a

  >>> from collections import Counter 
  >>> c = Counter(a=3, b=1)  
  >>> d = Counter(a=1, b=2)   
  >>> c-d  
  Counter({'a': 2})

zuminator

01d

I noticed that as well. Per the docs:

  Several mathematical operations are provided for combining Counter objects to produce multisets (counters that have counts greater than zero). Addition and subtraction combine counters by adding or subtracting the counts of corresponding elements. Intersection and union return the minimum and maximum of corresponding counts. Equality and inclusion compare corresponding counts. Each operation can accept inputs with signed counts, but the output will exclude results with counts of zero or less.

Anyway, nice Counter-example ;-)

brianwawok
1032d
I was so into Python for 10 years, was enjoyable to work in. But have deleted 100k+ lines this year already moving them to faster languages in a post AI codebot world. Mostly moving to go these days.
1. stuaxo
  22d
  This is straightforward in the first instance, but how do you see maintenance of those projects going forward - especially adding more complex features ?
  I can see one way forward being to prototype them in python and convert.
veqq
02d
There's a good interview about Python internals and management, particularly in relation to free-threading: https://alexalejandre.com/programming/interview-with-ngoldba...
drchaim
42d
Oh, my beloved Python, for nearly 15 years I wrote you. I miss you, but I no longer do — it's not your fault, life has changed.
1. speedster217
  02d
  I've really been enjoying modern Python both at work and on personal projects.
xg15
42d
> Iterators, async functions and async iterators don't work well here because they have different semantics to standard functions. When you call them they return immediately with a generator object, coroutine function and async generator object respectively. So the decorator completes immediately as opposed to the entire lifecycle what it's wrapping.
> This is an unfortunate problem I've encountered many times, and it's often a problem for normal decorators too. But this has changed in 3.15, now the ContextDecorator will check the type of the function it's wrapping and ensure that the decorator covers the entire lifespan.
I very much like the idea of that change - but it also seems kind of dangerous, to do this with no "opt-in mechanism", as that quite subtly changes the behavior of existing usage sites.
This is a bit of a "spacebar heating" situation, because someone would have to intentionally use a decorator in the old, broken way, but if someone actually did that, things may unexpectedly break.
1. ameliaquining
BiteCode_dev
02d
Note that 3.15 is not released yet. It will come out in 4 months
aniou
12d
I come to Python around version 1.5, painfully tired by debugging CGI scripts, created by wannabe perl-golfers. Unfortunately, I feel like Python is losing more and more of the zen that once tempted me...
Lazy loading looks like a last nail in the coffin, where my love to Python was buried, although it was a long, tiresome process.
1. t43562
  01d
  It's now being used by a lot of people because they have to rather than want to so there is a desire to ** it up and reinvent their favorite language by adding all sorts of warts. That's the price of success.
  A proper revenge would be to introduce "easy mode" to Rust - where the compiler takes a huge chill pill and you get non-enforced garbage collection. :-)
sunshine-o
62d
I am not a python dev but have the utmost respect for the ecosystem.
But damn, with all the supply chain attacks now in the news, could they just make a simple way (for non python insiders) to install python apps without fearing to be infected by a vermin with full access to my $HOME ...
1. nyrikki
  02d
  There is no security barrier at all in UNIX(-like) Os's between a caller/callee, this is not thing that python can just fix.
  There are ways to harden and/or reduce privileges, but shells/scripting languages will always have this issue on any modern OS.
  The UNIX way to help prevent that is really to run processes as another user, but people seem to refuse to do so. You should always expect any process running as your UID to be able to access any data owned or visible to your UID.
  While it is possible to reduce the risk of disclosure, they are all wack-a-mole preventions protecting the low hanging fruit, not absolute guarantees.
  That is purely due to how UNIX works [0]
  [0] https://man7.org/linux/man-pages/man7/credentials.7.html
danborn26
01d
These smaller features often end up being the most useful. I'm especially interested in testing the new standard library additions in my current projects.
frr149
61d
I used to be obsessed about language design and now, since I almost never write code directly (it's always Claude), I completely lost interest.
It feels like a total waste of time and I wonder if other feel the same.
One of the consequences of the LLM tsunami might be the freezing of research and development in programming languages.
Maybe we'll be stuck with J's and python forever...
1. inejge
  41d
  > I almost never write code directly (it's always Claude)
  Who, then, understands the code? If the answer is "no one really", entropy will overwhelm your codebase sooner or later. Otherwise, you need to read the code, and for that the knowledge of language is still relevant.
groundzeros2015
12d
Why does every language need every feature? Python has completely lost its charm.
1. t43562
  01d
  It's too popular and the people channeled into using it don't care about it other than to complain about why it isn't <insertlanguagehere>
axpy906
02d
When Wes McKinney wrote about the transition away from python I knew it was real. https://wesmckinney.com/blog/agent-ergonomics/
I still have a special place in my heart for the language and think it’s still got a niche.
armanj
32d
funny how we may have to wait even longer for llms to pick up this update in their pre-training
1. BiteCode_dev
  02d
  It's actually fantastic for job interviews. Use that trick with my clients when asked to review candidates.
syedMohib45
02d
Thread safe ittertors? really are we still on these topics
lazy from typing import Iterator
def stream_events(...) -> Iterator[str]: while True: yield blocking_get_event(...)
events = stream_events(...)
for event in events: consume(event)
vorsken
02d
The `except*` improvements are underrated. Been using ExceptionGroup in a CLI tool that wraps Semgrep — catching multiple subprocess errors cleanly in one block made the retry logic much simpler.
[deleted]
02d
[deleted]
JamesConnor_Dev
01d
[dead]
GeorgeTirebiter
21d
Absolutely serious question: is anybody actually writing code anymore? (Reviewing it, architecting it, sure -- we do that). But writing code? If NOT, then seems to me, what we want in our LLM output is CODE THAT IS TRIVIAL TO UNDERSTAND (I apologize for shouting from the rooftops.)
I'm not sure adding 'features' to Python anymore makes sense - UNLESS those features help humans understand LLM code. Part of the problem is, of course, that LLMs haven't been trained on the latest-and-greatest, so they won't output any of it (even new training events won't capture the latest very much, since there is so little of it relative to what is already out there).
But again -- do new features help HUMANS understand what the LLMs produce? If not, seems to me ... new features merely add complexity for no apparent gain. (Or am I confused about this?) THANKS for any helpful opinions.
1. GeorgeTirebiter
  01d

lazy from typing import Iterator def stream_events(...) -> Iterator[str]: while True: yield blocking_get_event(...) events = stream_events(...) for event in events: consume(event)

Several mathematical operations are provided for combining Counter objects to produce multisets (counters that have counts greater than zero). Addition and subtraction combine counters by adding or subtracting the counts of corresponding elements. Intersection and union return the minimum and maximum of corresponding counts. Equality and inclusion compare corresponding counts. Each operation can accept inputs with signed counts, but the output will exclude results with counts of zero or less.

# mise use node@24 # echo '{}' >package.json # npm i --save typescript # echo 'function Greeting({ name }: { name: string }) { return ( <div class="card"> <h1>Hello, {name}!</h1> <p>Welcome to my site.</p> </div> ); } ' >hello.tsx # : a test to check if we have a working typescript compiler # tsc hello.tsx error TS5112: tsconfig.json is present but will not be loaded if files are specified on commandline. Use '--ignoreConfig' to skip this error. # echo '{"compilerOptions":{"jsx":"react"}}' >tsconfig.json # tsc hello.tsx:1:58 - error TS7026: JSX element implicitly has type 'any' because no interface 'JSX.IntrinsicElements' exists. 1 function Greeting({ name }: { name: string }) { return ( <div class="card"> <h1>Hello, {name}!</h1> <p>Welcome to my site.</p> </div> ); } ~~~~~~~~~~~~~~~~~~ hello.tsx:1:59 - error TS2874: This JSX tag requires 'React' to be in scope, but it could not be found. 1 function Greeting({ name }: { name: string }) { return ( <div class="card"> <h1>Hello, {name}!</h1> <p>Welcome to my site.</p> </div> ); } ~~~ hello.tsx:1:77 - error TS7026: JSX element implicitly has type 'any' because no interface 'JSX.IntrinsicElements' exists. 1 function Greeting({ name }: { name: string }) { return ( <div class="card"> <h1>Hello, {name}!</h1> <p>Welcome to my site.</p> </div> ); } ~~~~ hello.tsx:1:78 - error TS2874: This JSX tag requires 'React' to be in scope, but it could not be found. 1 function Greeting({ name }: { name: string }) { return ( <div class="card"> <h1>Hello, {name}!</h1> <p>Welcome to my site.</p> </div> ); } ~~ hello.tsx:1:95 - error TS7026: JSX element implicitly has type 'any' because no interface 'JSX.IntrinsicElements' exists. 1 function Greeting({ name }: { name: string }) { return ( <div class="card"> <h1>Hello, {name}!</h1> <p>Welcome to my site.</p> </div> ); } ~~~~~ hello.tsx:1:101 - error TS7026: JSX element implicitly has type 'any' because no interface 'JSX.IntrinsicElements' exists. 1 function Greeting({ name }: { name: string }) { return ( <div class="card"> <h1>Hello, {name}!</h1> <p>Welcome to my site.</p> </div> ); } ~~~ hello.tsx:1:102 - error TS2874: This JSX tag requires 'React' to be in scope, but it could not be found. 1 function Greeting({ name }: { name: string }) { return ( <div class="card"> <h1>Hello, {name}!</h1> <p>Welcome to my site.</p> </div> ); } ~ hello.tsx:1:123 - error TS7026: JSX element implicitly has type 'any' because no interface 'JSX.IntrinsicElements' exists. 1 function Greeting({ name }: { name: string }) { return ( <div class="card"> <h1>Hello, {name}!</h1> <p>Welcome to my site.</p> </div> ); } ~~~~ hello.tsx:1:128 - error TS7026: JSX element implicitly has type 'any' because no interface 'JSX.IntrinsicElements' exists. 1 function Greeting({ name }: { name: string }) { return ( <div class="card"> <h1>Hello, {name}!</h1> <p>Welcome to my site.</p> </div> ); } ~~~~~~ Found 9 errors in the same file, starting at: hello.tsx:1 # cat hello.js function Greeting({ name }) { return (React.createElement("div", { class: "card" }, " ", React.createElement("h1", null, "Hello, ", name, "!"), " ", React.createElement("p", null, "Welcome to my site."), " ")); } # : sanity check # mise use deno # deno hello.tsx # : no output # echo 'function Greeting({ name }: { name: string }) { return ( <div class="card"> <h1>Hello, {name}!</h1> <p>Welcome to my site.</p> </div> ); }; Greeting({ name: "world!" });' >hello2.tsx # deno hello2.tsx error: Uncaught (in promise) ReferenceError: React is not defined at Greeting (file:////hellotsx/hello.tsx:1:49) at file:////hellotsx/hello.tsx:1:141