PEP 810 – Explicit lazy imports • Hacker News Board

Re: PEP 810 – Explicit lazy imports

#21

Post by charliermarsh » Fri, Oct 03, 2025, 7:35 PM UTC

Lazy imports have been proposed before, and were rejected most recently back in 2022: https://discuss.python.org/t/pep-690-lazy-imports-again/1966.... If I recall correctly, lazy imports are a feature supported in Cinder, Meta's version of CPython, and the PEP was driven by folks that worked on Cinder. Last time, a lot of the discussion centered around questions like: Should this be opt-in or opt-out? At what level? Should it be a build-flag for CPython itself? Etc. The linked post suggests that the Steering Council ultimately rejected it because of the complexity it would introduce to have two divergent "modes" of importing.

I hope this proposal succeeds. I would love to use this feature.

Re: PEP 810 – Explicit lazy imports

#22

Post by forrestthewoods » Fri, Oct 03, 2025, 7:36 PM UTC

I don’t want lazy imports. That’s just makes performance shitty later and harder to debug. It’s a hacky workaround.

What I want is for imports to not suck and be slow. I’ve had projects where it was faster to compile and run C++ than launch and start a Python CLI. It’s so bad.

Re: PEP 810 – Explicit lazy imports

#23

Post by oofbey » Fri, Oct 03, 2025, 7:37 PM UTC

TheMrZZ wrote: post #2

Feels like a good feature, with a simple explanation, real world use cases, and a scoped solution (global only, pretty simple keyword). I like it!

Hopefully they learned lessons from why PEP-690 was rejected. I've spent quite a while trying to build this stuff for our codebase and it's never worked well enough to use.

Re: PEP 810 – Explicit lazy imports

#24

Post by matsemann » Fri, Oct 03, 2025, 7:40 PM UTC

colpabar wrote: post #14

the__alchemist wrote: post #13

Does this fix the circular imports problem that comes up if you don't structural your programs in a hierarchical way?

This is what I thought of too. I really only know python, do other languages not have that issue? In python it does not seem like a "problem" to me - whenever I have seen circular import issues it is because the code is organized poorly. I worry that this feature will lead to devs "fixing" circular import issues by using lazy imports.

Sometimes it's hard to avoid cyclic imports, without blaming the design. Like if a Parent has a Child, and the Child needs to know of the parent. Only way to solve that in python is to put everything in the same file, which also feels like bad deisgn.

Re: PEP 810 – Explicit lazy imports

#25

Post by Alir3z4 » Fri, Oct 03, 2025, 7:40 PM UTC

I wish all imports were lazy by default.

I know/heard there are "some" (which I haven't seen by the way) libraries that depend on import side effects, but the advantage is much bigger.

First of all, the circular import problem will go away, especially on type hints. Although there was a PEP or recent addition to make the annotation not not cause such issue.

Second and most important of all, is the launch time of Python applications. A CLI that uses many different parts of the app has to wait for all the imports to be done.

The second point becomes a lot painful when you have a large application, like a Django project where the auto reload becomes several seconds. Not only auto reload crawls, the testing cycle is slow as well. Every time you want to run test command, it has to wait several seconds. Painful.

So far the solution has been to do the lazy import by importing inside the methods where it's required. That is something, I never got to like to be honest.

Maybe it will be fixed in Python 4, where the JIT uses the type hints as well /s

Re: PEP 810 – Explicit lazy imports

#26

Post by f311a » Fri, Oct 03, 2025, 7:43 PM UTC

I don't like the idea of introducing a new keyword. We need a backward compatible solution. I feel like Python needs some kind of universal annotation syntax such as in go (comments) or in Rust (macros). New keyword means all parsers, lsps, editors should be updated.

I’m pretty sure there will be new keywords in Python in the future that only solve one thing.

Re: PEP 810 – Explicit lazy imports

#27

Post by jeremyscanvic » Fri, Oct 03, 2025, 7:44 PM UTC

Really excited about this - we've recently been struggling with making imports lazy without completely messing up the code in DeepInverse https://deepinv.github.io/deepinv/

Re: PEP 810 – Explicit lazy imports

#28

Post by Spivak » Fri, Oct 03, 2025, 7:46 PM UTC

I love the feature but I really dislike using the word lazy as a new language keyword. It just feels off somehow. I think maybe defer might be a better word. It is at least keeps the grammar right because it would be lazily.

    lazily import package.foo
    vs
    defer import package.foo

Also the grammar is super weird for from imports.

    lazy from package import foo
    vs.
    from package defer import foo.

Re: PEP 810 – Explicit lazy imports

#29

Post by f311a » Fri, Oct 03, 2025, 7:48 PM UTC

Alir3z4 wrote: post #25

I wish all imports were lazy by default. I know/heard there are "some" (which I haven't seen by the way) libraries that depend on import side effects, but the advantage is much bigger. First of all, the circular import problem will go away, especially on type hints. Although there was a PEP or recent addition to make the annotation not not cause such issue. Second and most important of all, is the launch time of Pyth…

Lazy imports mean late errors. Fail fast is a good design principle.

Re: PEP 810 – Explicit lazy imports

#30

Post by the_mitsuhiko » Fri, Oct 03, 2025, 7:48 PM UTC

I like the approach of ES6 where you pull in bindings that are generally lazily resolved. That is IMO the approach that should be the general strategy for Python.