Comment on Python Performance: Why 'if not list' is 2x Faster Than Using len()

PattyMcB@lemmy.world ⁨11⁩ ⁨months⁩ ago

• WolfLink@sh.itjust.works ⁨11⁩ ⁨months⁩ ago

  I’ve worked on a library that’s Python because the users of said library are used to Python.

  The original version of the project made heavy use of numpy, so the actual performance sensitive code was effectively C++ and fourtran, which is what numpy is under the hood.

  We eventually replaced the performance sensitive part of the code with Rust (and still some fourtran because BLAS) which ended up being about 10x faster.

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• sugar_in_your_tea@sh.itjust.works ⁨11⁩ ⁨months⁩ ago

  Yes, Python is the wrong choice if performance is your top priority.

  But here’s another perspective: why leave easy performance wins on the table? Especially if the cost is simpler code that works as you probably wanted anyway with both None and []?

  Python is great if you want a really fast development cycle, because the code is generally quite simple and it’s “fast enough.” Any wins for “fast enough” is appreciated, because it delays me needing to actually look into little performance issues. It’s pretty easy for me to write a simple regex to fix this cose (s/if len\((\w+)\) == 0:/if not \1:/), and my codebase will be slightly faster. That’s awesome! I could even write up a quick pylint or ruff rule to catch these cases for developers going forward (if there isn’t one already).

  If I’m actively tweaking things in my Python code to get a little better performance, you’re right, I should probably just use something else (writing a native module is probably a better use of time). But the author isn’t arguing that you should do that, just that, in this case, if not foo is preferred over if len(foo) == 0 for technical reasons, and I’ll add that it makes a ton of sense for readability reasons as well.

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• Randelung@lemmy.world ⁨11⁩ ⁨months⁩ ago

  It comes down to the question “Is YOUR C++ code faster than Python?” (and of course the reverse).

  I’ve built a SCADA from scratch and performance requirements are low to begin with, seeing as it’s all network bound and real world objects take time to react, but I’m finding everything is very timely.

  A colleague used SQLAlchemy for a similar task and got abysmal performance. No wonder, it’s constantly querying the DB for single results.

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  • sugar_in_your_tea@sh.itjust.works ⁨11⁩ ⁨months⁩ ago

    Exactly!

    We rewrote some Fortran code (known for fast perf) into Python and the net result was faster. Why? They used bubble sort in a hot loop, whereas we used Python’s built-in sort (probably qsort or similar). So despite Python being “slower” on average, good architecture matters a lot more.

    And your Python code doesn’t have to be 100% Python, you can write performance-critical code in something else, like C++ or Rust. This is very common, and it’s why popular Python libraries like numpy and scipy are written in a more performant language with a Python wrapper.

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• pastermil@sh.itjust.works ⁨11⁩ ⁨months⁩ ago

  Because, while you don’t want to nitpick on each instruction cycle, sometimes the code runs millions of times and each microsecond adds up.

  Keep in mind that people use this kind of things for work, serving real world customers who are doing their work.

  Yes, the language itself is not optimal even by design, but its easy to work with, so they are making it worth a while. There’s no shortage of people who can work with it. It is easy to develop and maintain stuff with it, cutting development cost. Yes, we’re talking real businesses with real resource constraints.

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  • sugar_in_your_tea@sh.itjust.works ⁨11⁩ ⁨months⁩ ago

    Exactly. We picked it for the reasons you mentioned, and I still think it’s a good choice.

    That said, some of our heavier logic is in a lower-level language. We had some Fortran code until recently (rewrote in Python and just ate the perf cost to lower barrier to other devs fixing stuff), and we’re introducing some C++ code in the next month or two. But the bulk of our code is in Python, because that’s what glues everything together, and the code is fast enough for our needs.

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    • pastermil@sh.itjust.works ⁨11⁩ ⁨months⁩ ago

      People seem to be unaware that python has bindings for lower-level languages like C. In fact, people have been heavily using resource intensive libraries implemented in C (e.g. numpy, scipy, pandas, uwsgi).

      Also, Python interpreter performance has come a long way.

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• JustAnotherKay@lemmy.world ⁨11⁩ ⁨months⁩ ago

  Honestly most people use Python because it has fantastic libraries. They optimize it because the language is middling, but the libraries are gorgeous

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  • ThirdConsul@lemmy.ml ⁨11⁩ ⁨months⁩ ago

    Honestly most people use Python because it has fantastic libraries

    In C++ if I remember correctly…

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    • JustAnotherKay@lemmy.world ⁨11⁩ ⁨months⁩ ago

      What do I care what language the library is written in as long as it works for what I need it do?

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      • ThirdConsul@lemmy.ml ⁨11⁩ ⁨months⁩ ago

        My point is tha the libraries itself are not in Python and thus most likely not exclusive to it. This is not an attack on Python, I just find it funny a bit :)

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      • sugar_in_your_tea@sh.itjust.works ⁨11⁩ ⁨months⁩ ago

        Exactly! Most of the important libraries in other languages have Python support. So I can use Python and not care if they wrote the library in C++, Rust, or something more exotic, provided it works in Python.

        Python is more about gluing stuff together than writing a bunch of greenfield logic. If you run into performance problems and you’re using Python, the best solution is to start rewriting the slow parts in something faster, not to rewrite the whole thing in something different.

        That said, most of my personal projects are in Rust, for a variety of reasons. But I still use a lot of Python as well, and it’s what I use 99% of the time at work.

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• jerkface@lemmy.ca ⁨11⁩ ⁨months⁩ ago

  Alternatively, why wait twice as long for your python code to execute as you have to?

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• lengau@midwest.social ⁨11⁩ ⁨months⁩ ago

  It’s all about trade-offs. Here are a few reasons why one might care about performance in their Python code:

  1. Performance is often more tied to the code than to the interpreter - an O(n³) algorithm in blazing fast C won’t necessarily perform any better than an O(nlogn) algorithm in Python.
  2. Just because this particular Python code isn’t particularly performance constrained doesn’t mean you’re okay with it taking twice as long.
  3. Rewriting a large code base can be very expensive and error-prone. Converting small, very performance-sensitive parts of the code to a compiled language while keeping the bulk of the business logic in Python is often a much better value proposition.

  These are also performance benefits one can get essentially for free with linter rules.

  Anecdotally: in my final year of university I took a computational physics class. Many of my classmates wrote their simulations in C or C++. I would rotate between Matlab, Octave and Python. During one of our labs where we wrote particle simulations, I wrote and ran Octave and Python simulations in the time it took my classmates to write their C/C++ versions, and the two fastest simulations in the class were my Octave and Python ones, respectively. (The professor’s own sim came in third place). The overhead my classmates had dealing with poorly optimised code that caused constant cache misses was far greater than the interpreter overhead in my code (though at the time I don’t think I could have explained why their code was so slow compared to mine).

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  • uis@lemm.ee ⁨11⁩ ⁨months⁩ ago

    1. Performance is often more tied to the code than to the interpreter - an O(n³) algorithm in blazing fast C won’t necessarily perform any better than an O(nlogn) algorithm in Python.

    An O(n³) algorithm in Python won’t necessarily perform any better than an O(nlogn) algorithm in C. Ever heard of galactic algorithms?

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  • PattyMcB@lemmy.world ⁨11⁩ ⁨months⁩ ago

    I appreciate the large amount of info. Great answer. It just doesn’t make sense to me, all things being equal (including performant algorithms), why choose Python and then make a small performance tweak like in the article? I understand preferring the faster implementation, but it seems to me like waxing your car to reduce wind resistance to make it go faster, when installing a turbo-charger would be much more effective.

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    • 0ops@lemm.ee ⁨11⁩ ⁨months⁩ ago

      If anything, to me it seems more important for a slower language to be optimized. Ideally everything would be perfectly optimized, but over-optimization is a thing: making optimizations that aren’t economical. Even though c is many times faster than python, for many projects it’s fast enough that it makes no practical difference to the user. They’re not going to bitch about a function taking 0.1 seconds to execute instead of 0.001, but they might start to care when that becomes 100 seconds vs 1. As the program becomes more time intensive to run, the python code is going to hit that threshold where the user starts to notice before c, so economically, the python would need to be optimized first.

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    • Teanut@lemmy.world ⁨11⁩ ⁨months⁩ ago

      If you use the profiler and see that the slower operation is being used frequently, and is taking up a chunk of time deemed significant, why not swap it to the faster version?

      In a simulation I’m working on that goes through 42 million rounds I spent some time profiling and going through the code that was eating up a lot of time (especially things executed all 42 million times) and trying to find some optimizations. Brought the run time down from about 10 minutes to 5 minutes.

      I certainly wasn’t going to start over in C++ or Rust, and if I’d started with either of those languages I would have missed out on a lot of really strong Python libraries and probably spent more time coding rather than refining the simulation.

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    • lengau@midwest.social ⁨11⁩ ⁨months⁩ ago

      I think a better analogy would be that you’re tuning your bike for better performance because the trade-offs of switching to a car are worse than keeping the bike.

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      • PattyMcB@lemmy.world ⁨11⁩ ⁨months⁩ ago

        Ok… I’ll buy that

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• Takapapatapaka@lemmy.world ⁨11⁩ ⁨months⁩ ago

  You may want to beneficiate from little performance boost even though you mostly don’t need it and still need python’s advantages. Being interested in performance isnt always looking for the very best performance there is out of any language, it can also be using little tips to go a tiny bit faster when you can.

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• Reptorian@lemmy.zip ⁨11⁩ ⁨months⁩ ago

  I have the same question. I prefer other languages. I use G’MIC for image processing over Python and C++.

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