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)
3.15: https://docs.python.org/3.15/whatsnew/3.15.html#whatsnew315-...
> 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.
It's unrelated to the lazy keyword. Instead it's another feature related to error messages.
The example:
In the Rust toolchain we've done the same. It just so happens that rustdoc already has introduced annotations for "aliases" so that when someone searches for push and it doesn't exist, append would show up. Having those annotations already meant that bootstrapping the feature to check the aliases during name resolution errors in rustc was almost trivial. I love it when improving one thing improves another indirectly too.
I really appreciate them going out of their way to do this, being quite aware of the hidden complexity in doing it.
I’ve often thought it would be funny if instead of an error message for stuff like this, a language could be designed to be “typo-insensitive”. If a method or function call is similar enough to an existing one or a common one from other languages, to just have it silently use that.
VisualBasic did that. I think it is a mistake. But that doesn't mean that the compiler can't detect that and tell you how to fix it instead.
Sure VB ignores case, but what I want is for it to compare each method against a dictionary of similar terms. And maybe calculate the Levenshtein distance between all terms if it’s not found, and just assume it’s the closest one. You could also assume that full-width characters or similar-looking glyphs are equivalent (BASIC was pre-Unicode, so I can forgive them for not including that).
Lisp had a package for that, DWIM, in the late 60s: https://en.wikipedia.org/wiki/DWIM.
I hope you mean "funny" in the "hilarity ensues" sense.
Because the alternative is a rather sociopathic level of schadenfreude.
Yes, I say “funny” because it would be impractical and weird, definitely not a good idea. It’s already a bad enough that so many popular languages don’t (and can’t) check if a field or method is misspelled at compile time…
Now I'm wishing for a single cross-language library, that I can somehow inject into every compiler/runtime/checker to get this, but with a single source of truth and across a wide range of languages. I hit this damn issue all the time, writing code in one language for another, would truly be a bliss to have that problem solved once and for all.
If you had a "canonical datastructure database", you could have very short annotations on every standard library for any language that indexes a function to their canonical name. After that you only need to update the database.
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?
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.
Ah, thanks for the update. My only check before asking was to check if the future feature for annotations had been enabled by default yet. It has then effectively been abandoned instead, I guess.
Yup, "from __future__ import annotations" will eventually be removed:
> from __future__ import annotations (PEP 563) will continue to exist with its current behavior at least until Python 3.13 reaches its end-of-life. Subsequently, it will be deprecated and eventually removed.
So the future behavior is deprecated before it ever became the default?
It was an abandoned path even before 3.10, it just took longer to implement 649 and 749 than they expected.
But this is a "...will continue to exist with its current behavior at least..." is an important bit there.
From pep-0749:
It has a good overview of the history.https://peps.python.org/pep-0749/
Correct. Before the "from __future__ import annotations" behavior that converts annotations to strings became the default, they figured out a better mechanism for circular type annotations (making them lazy) that is implicitly backwards compatible and that didn't need to be guarded behind a future statement.
Ironically, the new default behavior (making type annotation evaluation lazy) is not backwards compatible with the "from __future__ import annotations" behavior of converting annotations to strings, so they can't just rip out "from __future__ import annotations" and instead it needs to be deprecated and removed over multiple releases.
Oh, what tangled webs we weave! :-)
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Note that you can work around it by implementing `def __getattr__(name: str) -> object:` at the module level on earlier Python versions
Somehow I have no trouble imagining this being used as a rationale to avoid unnecessary "magic" to the language for years
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Yes, 3.15+
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Python is such a weird language. Lazy imports are a bandaid for AI code base monstrosities with 1000 imports (1% of which are probably Shai Hulud now).
And now even type imports are apparently so slow that you have to disable them if unused during the normal untyped execution.
If Instagram or others wants a professional language, they should switch to Go or PHP instead of shoehorning strange features into a language that wasn't built for their use cases.
> 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.
I think this is just a natural consequence of an easy-to-use package system. The exact same story as with node. If you don't want lots of imports, don't make it so damn easy to pile them into projects. I'm frankly surprised we still see so few supply chain attacks, even though they picked up their cadence dramatically.
IIUC the organizations that most strongly pushed for this feature are big companies with large codebases. These tend not to be the kinds of orgs that just casually pull in dependencies from PyPI on a whim; I think it more likely that the quantity of first-party code was so large that importing all of it on startup was causing problems.
This seems a lot more due to an import running arbitrary code because stuff can happen in the top-level of a module rather than only happening in functions. From what I can tell, it seems pretty common for dynamically typed languages and pretty much entirely absent from statically typed ones, which tend to have a main function that everything else happens inside transitively. I guess this makes it easy if what you're writing is something that runs with no dependencies, but it's a pretty terrible experience as soon as you try to introduce the concept of a library.
> it seems pretty common for dynamically typed languages and pretty much entirely absent from statically typed ones
Counter-example is Go and init() function.
Interesting, I had no idea that existed! I still think there's a a difference between "here's a hook you can use to run stuff earlier" and "importing any module is fundamentally the same as running it as a script unless the module happens to use a special conditional to wrap stuff inside of" though (and I say this as someone who doesn't go out of his way to defend Go design decisions)
Also C++/Java static initialization, C# static constructors, or Rust global variable initialization, ...
Most languages have this feature Afaik
What would your alternative look like?
Too much syntactic sugar causes cancer of the semicolon.
True, but this is yet another code path that isn't exercised until specific conditions happen. That means even more latent application behaviour can go undetected by unit testing and security profiling until the moon is in the right phase, which is a boon for submarine attacks.
Empirically, I have used the current accepted way to do lazy imports (import statement inside a function) before AI coding was even a mainstream thing, for personal code that sometimes needs a heavy import and sometimes doesn’t.
The lazy statement would be an improvement as it allows one to see all the imports at the top where you expect them to be.
As a now deleted comment pointed out, lazy imports had been requested forever. They were rejected forever and were accepted just when BigCorps wanted them.
Python-dev now is paid to shore up the failed Instagram stack.
both lazy imports and free threading have been proposed ages ago, they both went through several iterations before a good design was settled upon and made it into the language.
in the case of lazy imports the big corps were the ones doing the experimentation and iteration. the feature didn't make it into the language "just when big corps wanted them"; the instagram stack you allude to already had its own fork of cpython with lazy imports added years ago, and that is not the design that ended up getting adopted by upstream cpython, though some of the people working on it also collaborated on the PEP that finally did make it in.
It was accepted just as multiple large corporations with competent teams of internal tool departments ended up forking the interpreter to support lazy imports and demonstrated empirically that the idea has merit.
I too am outraged that a product would prioritize its biggest users.
Is the biggest user larger than the combined set of individual users who had asked for (or would benefit from) the same thing? I honestly don't know, but I don't think that things are always as simple as you're implying in a world where we have the collective action problem.
If you’re asking some some kind of abstract moral value sense, I have idea.
If you’re asking whether project leads give more weight to a single, tangible, vocal stakeholder than they do to unknown numbers of anonymous and lightly-engaged stakeholders? Yes.
Not to mention when the single, tangible, vocal stakeholder can also be asked to be responsible for documentation (PEPs, etc) and PRs. Especially in open source there is a huge difference between "a lot of people asked about this" and "one person asked about this, but was passionate enough about it and open enough to following the process and the feedback loops to champion it all the way across the finish line".
I don't have any issue with what you're saying if that's what happened. There's quite a gap between that sort of reasoned explanation and treating concerns about large stakeholders versus large numbers of small one with derision.
For what it is worth, I was trying not to make a value judgment on it, especially not with relation to this specific instance, I was hopefully just recognizing it as a motivating factor in general open source politics. Sometimes that is quite regretful because it is anti-democratic and does look like favoritism or worse cronyism when it plays out in that way of "we listened to the person/company that built and tested a prototype and did all the work to standardize and then PR it over the many developers that wanted an idea but didn't have the time/money/bandwidth to implement it themselves".
I mean, yes, demonstrably, the phenomenon you're describing happens. Your previous comment seems pretty sarcastically dismissing the idea that someone could disagree with this being a good thing though, and I was making a counterargument against the underlying opinion that seemed apparent.
On most unix-likes all "imports" via shared libraries (e.g. in C / C++) are lazy by default.
But also great for speed. Larger libraries can take a measurable amount of time to import (even if they have no transitive dependencies). If only some of your code paths actually need the large library then it makes sense to import it lazily. Without lazy you have to do it conditionally which can lead to the imports happening in strange places rather than all being listed out at the top of the file.