Why Python Is So Slow (And What Is Being Done About It) (thenewstack.io)

submitted 5 months ago by dominiquec@lemmy.world to c/python@programming.dev

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[-] MalReynolds@slrpnk.net 65 points 5 months ago* (last edited 5 months ago)

When you need speed in Python, after profiling, checking for errors, and making damn sure you actually need it, you code the slow bit in C and call it.

When you need speed in C, after profiling, checking for errors, and making damn sure you actually need it, you code the slow bit in Assembly and call it.

When you need speed in Assembly, after profiling, checking for errors, and making damn sure you actually need it, you're screwed.

Which is not to say faster Python is unwelcome, just that IMO its focus is frameworking, prototyping or bashing out quick and perhaps dirty things that work, and that's a damn good thing.

[-] dgriffith@aussie.zone 22 points 5 months ago* (last edited 5 months ago)

Generally I bash together the one-off programs in Python and if I discover that my "one off" program is actually being run 4 times a week, that's when I look at switching to a compiled language.

Case in point: I threw together a python program that followed a trajectory in a point cloud and erased a box around the trajectory. Found a python point cloud library, swore at my code (and the library code) for a few hours, tidied up a few point clouds with it, job done.

And then other people in my company also needed to do the same thing and after a few months of occasional use, I rewrote it using C++ and Open3D. A few days of swearing this time (mainly because my C++ is a bit rusty, and Open3D's C++ interface is a sparsely-documented back end to their main python front end).

End result though is that point clouds that took 3 minutes to process before in python now take 10 seconds, and now there's a visualisation widget that shows the effects of the processing so you don't have to open the cloud in another viewer to see that it was ok.

But anyway, like you said, python is good for prototyping, and when you hash out your approach and things are fairly nailed down and now you'd like some speed, jump to a compiled language and reap the benefits.

[-] balder1993@programming.dev 6 points 5 months ago* (last edited 5 months ago)

And at that point you’ll also have a better idea of the problem and solution.

[-] sugar_in_your_tea@sh.itjust.works 4 points 5 months ago

Python is also pretty good for production, provided you're using libraries optimized in something faster. Is there a reason you didn't use Open3D's Python library? I'm guessing you'd get close to the same performance of the C++ code in a lot less time.

That said, if you're doing an animation in 3D, you should probably consider a game engine. Godot w/ GDScript would probably be good enough, though you'd spend a few days learning the engine (but the next project would be way faster).

If you're writing a performance-critical library, something compiled is often the better choice. If you're just plugging libraries together, something like Python is probably a better use of your time since the vast majority of CPU time can generally be done in a library.

[-] sugar_in_your_tea@sh.itjust.works 15 points 5 months ago* (last edited 5 months ago)

I'd really like to see Rust fit in where C(++) does now for Python. I know some libraties do it (e.g. Pydantic), but it really should be more common. It should work really well with the GIL... (or the TIL or whatever the new one is)

[-] barnaclebutt@lemmy.world 4 points 5 months ago* (last edited 5 months ago)

Or you could use cython, which is much easier to integrate with a python project. It is only marginally slower than Rust but a little less safe. Numpy libraries are usually the fast. Numba is a little clunky, but can also speed up code. There's lots of options to speed up python code.

[-] sugar_in_your_tea@sh.itjust.works 2 points 5 months ago

Yup, Cython rocks.

You can also use numba if you just need to accelerate one part of the app. We did that with a heavy part of the app and our naïve Python (using numpy) was about as fast as our naïve Rust, but only when wr turned on parallel processing in numba (I could've easily beat it with parallel Rust, but that requires extra work and wouldn't fit as nicely into the rest of the app).

[-] MalReynolds@slrpnk.net 4 points 5 months ago

Sounds like an excellent idea, I'd be surprised if it isn't happening.

[-] sugar_in_your_tea@sh.itjust.works 3 points 5 months ago

Well, it is happening, I just don't know how "blessed" it is by Python maintainers (i.e. are Python releases blocked by Rust binding updates?). It's 100% possible today and there are projects that use Rust bindings, I just don't know how that fits in with Python development vs the C++ API.

[-] souperk@reddthat.com 15 points 5 months ago* (last edited 5 months ago)

While I agree with most of what you say, I have a personal anecdote that highlights the importance of performance as a feature.

I have a friend that studies economics and uses python for his day to day. Since computer science is not his domain, he finds it difficult to optimize his code, and learning a new language (C in this case) is not really an option.

Some of his experiments take days to run, and this is becoming a major bottleneck in his workflow. Being able to write faster code without relying on C is going to have a significant impact on his research.

Of course, there are other ways to achieve similar results, for example another friend is working on DIAS a framework that optimizes pandas in the runtime. But, the point still stands, there are a tonne of researchers relying on python to get quick and dirty results, and performance plays a significant in that when the load of data is huge.

[-] MalReynolds@slrpnk.net 8 points 5 months ago

Sure, I was being mildly facetious, but pointing to a better pattern, the nature of python means it is, barring some extreme development, always going to be an order of magnitude slower than compiled. If you're not going to write even a little C, then you need to look for already written C / FORTRAN / (SQL for data) / whatever that you can adapt to reap those benefits. Perhaps a general understanding of C and a good knowledge of what your Python is doing is enough to get a usable result from a LLM.

[-] sugar_in_your_tea@sh.itjust.works 6 points 5 months ago* (last edited 5 months ago)

I have an alternative anecdote.

My coworker is a Ph.D in something domain specific, and he wrote an app to do some complex simulation. The simulation worked well on small inputs (like 10), but took minutes on larger inputs (~100), and we want to support very large inputs (1000+) but the program would get killed with out of memory errors.

I (CS background) looked over the code and pointed out two issues:

bubble sort in a hot path
allocated all working memory at the start and used 4D arrays, when 3D arrays and a 1D result array would've sufficed (O(n^4^) -> O(n^3^))

Both problems would have been solved had they used Python, but they used Fortran because "fast," but it doesn't have builtin sort or data structures. Python provides classes, sortable lists (with quicksort!), etc, so they could've structured their code better and avoided the architectural mistakes that caused runtime and memory to explode. Had they done that, I could've solved performance problems by switching lists to numpy arrays and throwing numba on the hot loops and been done in a day, but instead we spent weeks rewriting it (nobody understands Fortran, and that apparently included the original dev).

Python lets you focus on the architecture. Compiled languages often get you stuck in the weeds, especially if you don't have a strong CS background and just hack things until it works.

[-] Diplomjodler3@lemmy.world 35 points 5 months ago

In all the stuff I do in Python, runtime is not a consideration at all. Developer productivity is far more of a bottleneck. Having said that, I do of course see the value in these endeavours.

[-] FizzyOrange@programming.dev 9 points 5 months ago

If everyone had a magic lamp that told them whether performance was going to be an issue when they started a project then maybe it wouldn't matter. But in my experience people start Python projects with "performance doesn't matter", write 100k lines of code and then ask "ok it's too slow now, what do we do". To which the answer is "you fucked up, you shouldn't have used Python".

[-] sugar_in_your_tea@sh.itjust.works 6 points 5 months ago

No, it's usually "microservices" or "better queries" or something like that. Python performance shouldn't be an issue in a well-architected application. Source: I work on a project with hundreds of thousands of lines of Python code.

[-] hark@lemmy.world 4 points 5 months ago

That depends on what the application needs to do. There's a reason why all performance-critical libraries for Python aren't written in Python.

[-] sugar_in_your_tea@sh.itjust.works 3 points 5 months ago

Sure, and we use those, like numpy, scipy, and tensorflow. Python is best when gluing libraries together, so the more you can get out of those libraries, the better.

Python isn't fast, but it's usually fast enough to shuffle data from one library to the next.

[-] hark@lemmy.world 4 points 5 months ago

Usually, but when it isn't then you've got a bottleneck. Multithreaded performance is a major weak point if you need to do any processing that isn't handled by one of the libraries.

[-] sugar_in_your_tea@sh.itjust.works 2 points 5 months ago* (last edited 5 months ago)

Then you need to break up your problem into processes. Python doesn't really do multi-threading (hopefully that changes with the GIL going away), but most things can scale reasonably well in a process pool if you manage the worker queue properly (e.g. RabbitMQ works well).

It's not as good as proper threadimg, but it's a lot simpler and easier to scale horizontally. You can later rewrite certain parts if hosting costs become a larger issue than dev costs.

[-] hark@lemmy.world 3 points 5 months ago

A process pool means extra copying of data around which incurs a huge cost and this is made worse by the tendency for parallel-processing-friendly workloads often consisting of large amounts of data.

[-] sugar_in_your_tea@sh.itjust.works 2 points 5 months ago

Yup, which is why you should try to limit the copying by designing your parallel processing algorithm around it. If you can't, you would handle threading with a native library or something and scale vertical instead of horizontal. Or pick a different language if it's a huge part of your app.

But in a lot of cases, it's reasonable to stick with Python and scale horizontally. That has value if you're otherwise a Python shop.

[-] Valmond@lemmy.world 4 points 5 months ago

100k lines of code doesn't mean anything.

You can make a 1k python lines bog down your new shiny PC, as well 1M lines run just fine.

[-] sugar_in_your_tea@sh.itjust.works 2 points 5 months ago* (last edited 5 months ago)

Exactly. We have hundreds of thousands of lines of code that work reasonably well. I think we made the important decisions correctly, so performance issues in one area rarely impact others.

We rewrote ~1k lines of poorly running Fortran code into well-written Python code, and that worked because we got the important parts right (reduced big-O CPU from O(n^3^) to O(n^2^ log n) and memory from O(n^4^) to O(n^3^)). Runtime went from minutes to seconds in medium size data sets, and made large data sets possible to run (those would OOM due to O(n^4^) storage in RAM). If you get the important parts right, Python is probably good enough, and you can get linear optimizations from there by moving parts to a compiled language (or use a JIT like numba). Python wasn't why we could make it fast, it's just what we prototyped with so we could focus on the architecture, and we stopped optimizing when it was fast enough.

[-] FizzyOrange@programming.dev 1 points 5 months ago

Well yeah if by "well architected" you mean "doesn't use Python".

"microservices” or “better queries"

Not everything is a web service. Most of the slow Python code I encounter is doing real work.

[-] sugar_in_your_tea@sh.itjust.works 3 points 5 months ago

We also do "real work," and that uses libraries that use C(++) under the hood, like scipy, numpy, and tensorflow. We do simulations of seismic waves, particle physics simulations, etc. Most of our app is business logic in a webapp, but there's heavy lifting as well. All of "our" code is Python. I even pitched using Rust for a project, but we were able to get the Python code "fast enough" with numba.

We separate expensive logic that can take longer into background tasks from requests that need to finish quickly. We auto-scale horizontally as needed so everything remains responsive.

That's what I mean by "architected well," everything stays responsive and we just increase our hosting costs instead of development costs. If we need to, we could always rewrite parts in a faster language, provided that costs less than the development costs. We really don't spend much time at all optimizing python code, so we're not at that point yet.

That being said, I do appreciate faster-running code. I use Rust for most of my personal projects, but that's because I don't have to pay a team to maintain my projects.

[-] FizzyOrange@programming.dev 1 points 5 months ago

Matrix code is the very best case for offloading work from Python to something else though.

Think about something like a build system (e.g. scons) or a package installer (pip). There is no part of them that you can point to and say "that's the slow bit, write it in C" because the slowness is distributed through the entire thing.

[-] sugar_in_your_tea@sh.itjust.works 1 points 5 months ago

Both of those are largely bound by i/o, but with some processing in between, so the best way to speed things up is probably am async i/o loop that feeds a worker pool. In Python, you'd use processes, which can be expensive and a little complicated, but workable.

And as you pointed out, scons and pip exist, and they're fast enough. I actually use poetry, and it's completely fine.

You could go all out and build something like cargo, but it's the architecture decisions that matter most in something i/o bound like that.

[-] FizzyOrange@programming.dev 1 points 5 months ago

they’re fast enough

Strong disagree. I switched from pip to uv and it sped my install time up from 58 seconds to 7. Yeah really. If pip is i/o bound where is all that speed up coming from?

[-] sugar_in_your_tea@sh.itjust.works 1 points 5 months ago

That's pretty impressive! We have a bunch of a bunch of compiled stuff (numpy, tensorflow, etc), so I'm guessing we wouldn't see as dramatic of an improvement.

Then again, <1 min is "good enough" for me, certainly good enough to not warrant a rewrite. But I'll have to try uv out, maybe we'll switch to it. We switched from requirements.txt -> pyproject.toml using poetry, so maybe it's worth trying out the improved pyproject.toml support. Our microservices each take ~30s to install (I think w/o cache?), which isn't terrible and it's a relatively insignificant part of our build pipelines, but rebuilding everything from scratch when we upgrade Python is a pain.

[-] FizzyOrange@programming.dev 1 points 5 months ago

Yeah I was very impressed. The only problem with uv and third party tools in general is that the main reason we're using Python is because my boss didn't want people to have to install extra stuff to use it. I would prefer using Deno, but apparently a one-line rock solid install command is too much to ask compared to the mess of Python infra... smh.

[-] sugar_in_your_tea@sh.itjust.works 1 points 5 months ago

Well, I'm kind of the boss, but I inherited the Python codebase. The original reasoning was it's easier to hire/on-board people, which I think is largely true.

If it was up to me, I'd rewrite a bunch of our code to Rust. I use it for personal projects already, so I know the ecosystem. But that's a tough sale to the product team, so it's probably not happening anytime soon. I'd also have to retrain everyone, which doesn't sound fun...

However, any change I make needs to work smoothly for our devs, and we have a few teams across 3 regions. So it needs clear advantages and whatnot to go through the pain of addressing everyone's concerns.

[-] FizzyOrange@programming.dev 1 points 5 months ago

that’s a tough sale to the product team

Sounds like you're not the boss enough!

I agree Rust has a pretty steep learning curve so it's definitely reasonable to worry about people learning it, especially existing employees. Though I don't really buy the "easier to hire people" argument. There are plenty of Rust developers actively looking for Rust jobs, so I suspect you get fewer candidates but the ones you do get are higher quality and more interested.

But anyway I don't think that argument holds for Deno. Typescript is in the same difficulty league as Python. Anyone that knows Python should be able to transition easily.

[-] sugar_in_your_tea@sh.itjust.works 1 points 5 months ago* (last edited 5 months ago)

Yup, I guess not. But if I was on the product team, the customers and director ate the bosses. And on it goes up to the CEO, where the board and shareholders are the boss.

If I can justify the change, we'll do it. That's close enough for me. And I did do a POC w/ Rust and could've switched one service over, but I campaigned against myself since we got good enough perf w/ Python (numpy + numba) and I was the only one who wanted it. That has changed, so I might try again with another service (prob our gateway, we have 3 and they all kinda suck).

I'll have to check out Deno again. I remember looking at it (or something like it) a couple years ago when first announced on Reddit.

[-] FizzyOrange@programming.dev 1 points 5 months ago

Yeah I have yet to really use Deno in anger because so many people are like "but Python exists!" and unsurprisingly we now find ourselves with a mess of virtual environments and pip nonsense that has literally cost me weeks of my life.

Though if you're using Numpy that source like "proper work" not the infrastructure scripting we use Python for so I probably would go with Rust over Deno. I don't know of mature linear algebra libraries for Typescript (though I also haven't looked).

IMO probably the biggest benefit of Rust over most languages is the lower number of bugs and reduced debugging time due to the "if it compiles it probably works" thing.

[-] sugar_in_your_tea@sh.itjust.works 1 points 5 months ago* (last edited 5 months ago)

You don't have to convince me that Rust rocks. I just need to convince my team that it's worth the investment in terms of time to onboard everyone, time to port out application, and risk of introducing bugs.

We have a complex mix of CRUD, math-heavy algorithms, and data transformation logic. Fortunately, each of those are largely broken up into microservices, so they can be replaced as needed. If we decide to port, we can at least do it a little at a time.

The real question is, does the team want to maintain a Python or Rust app, and since almost nobody on the team has professional experience with low-level languages and our load is pretty small (a few thousand users; b2b), Python is preferred.

[-] mapto@lemmy.world 4 points 5 months ago

Q: what do we do? A: profile and decompose. Should not be that distant as a thought

[-] FizzyOrange@programming.dev 1 points 5 months ago

Profiling is an extremely useful tool for optimising the system that you have. It doesn't help if you have the wrong system entirely though.

[-] sugar_in_your_tea@sh.itjust.works 2 points 5 months ago

That's why you need an architect to design the project for the expected requirements. They'll ask the important questions, like:

how many users (if it's a server)
any long-running processes? If so, what will those be doing?
how responsive does it need to be? What's "fast enough"?
what's more important short term, feature delivery or performance? Long term? How far away is "long term"?
what platforms do we need to support?
is AI or similar in the medium term goals? What's the use case?
how bad is downtime? How much are you willing to spend if downtime isn't an option?

You don't need all the answers up front, but you need enough to design a coherent system. It's like building a rail system, building a commuter line is much different than a light rail network, and the planners will need to know if those systems need to interact with anything else.

If you don't do that, you're going to end up overspending in some area, and probably significantly.

[-] mapto@lemmy.world 2 points 5 months ago

Upfront analysis and design is very close to independent from the technology, particularly at the I/O level

[-] erp@lemmy.world 24 points 5 months ago

Why on earth would we try to make snakes faster? Science has gone too far this time. What's next, give them arms?

[-] sugar_in_your_tea@sh.itjust.works 5 points 5 months ago

Wings.

[-] Ephera@lemmy.ml 20 points 5 months ago

The aim is to offer the speed of C or C++ while retaining the user-friendly feel of Python itself.

These kind of claims always annoy me. Like, sure, there's some room for interpretation there, but at the end of the day, C, C++ and also Rust achieve their speed by having handling baked into the semantics for:

non-GC memory management
passing by-reference vs. by-value
and in the case of Rust, also for handling multi-threaded processing.

Unless he comes up with a revolutionary new memory management strategy, or achieves a massive jump in static analysis to replace human intelligence, then you simply can't achieve similar speed while keeping the semantics of Python.

[-] FizzyOrange@programming.dev 6 points 5 months ago

That's not really true. C# and Java are reference-based, uses GC and can be multithreaded, and are very comparable to Rust/C++/C performance. Certainly no more than twice as bad. Whereas Python is probably 50x as bad.

The real answer is that Python developers have deliberately avoided worrying about performance when designing the language, until maybe 2 years ago. That means it has ended up being extremely dynamic and difficult to optimise, and the CPython implementation itself has also not focused on performance so it isn't fast.

But I agree the aim of offering C/C++ speed is never going to be met with Python syntax.

[-] sugar_in_your_tea@sh.itjust.works 2 points 5 months ago

They can probably beat or at least match Javascript, which has been heavily optimized, but the cap is going to be something like Lua (not LuaJit) without significant, painful changes.

If you want faster Python today, you can try numba or Cython, both solve the problem in a different way with different tradeoffs.