6 ms·
A lot of people here are commenting that if you have to care about specific latency numbers in Python you should just use another language. I disagree. A lot o
by thundergolfer 9mo ago
A lot of people here are commenting that if you have to care about specific latency numbers in Python you should just use another language.
I disagree. A lot of important and large codebases were grown and maintained in Python (Instagram, Dropbox, OpenAI) and it's damn useful to know how to reason your way out of a Python performance problem when you inevitably hit one without dropping out into another language, which is going to be far more complex.
Python is a very useful tool, and knowing these numbers just makes you better at using the tool.
The author is a Python Software Foundation Fellow. They're great at using the tool.
In the common case, a performance problem in Python is not the result of hitting the limit of the language but the result of sloppy un-performant code, for example unnecessarily calling a function O(10_000) times in a hot loop.
I wrote up a more focused "Python latency numbers you should know" as a quiz here https://thundergolfer.com/computers-are-fast https://thundergolfer.com/computers-are-fast
- nutjob2 9mo ago> A lot of important and large codebases were grown and maintained in Python How does this happen? Is it just inertia that cause people to write large systems in a essentially type free, interpreted scripting language?
- oofbey 9mo agoIt’s very natural. Python is fantastic for going from 0 to 1 because it’s easy and forgiving. So lots of projects start with it. Especially anything ML focused. And it’s much harder to change tools once a project is underway.
- passivegains 9mo agothis is absolutely true, but there's an additional nuance: yes, python is fantastic, yes, it's easy and forgiving, but there are other languages like that too. ...except there really aren't. other than ruby and maybe go, every other popular language sacrifices ease of use for things that simply do not matter for the overwhelming majority of programs. much of python's popularity doesn't come from being easy and forgiving, it's that everything else isn't. for normal programming why would we subject ourselves to anything but python unless we had no choice? while I'm on the soapbox I'll give java a special mention: a couple years ago I'd have said java was easy even though it's tedious and annoying, but I've become reacquainted with it for a high school program (python wouldn't work for what they're doing and the school's comp sci class already uses java.) this year we're switching to c++.
- zelphirkalt 9mo agoOmg, switching to C++ for pupils programming beginners ... "How to turn off the most students from computer programming?" 101. Really can't get much worse than C++ for beginners.
- nightfly 9mo agoPSU (Oregon) uses C++ as just "c with classes" and ignores the rest of C++ for intro to programming courses. It frustrates people who already use C++ but otherwise works pretty well.
- Izkata 9mo agoThis was how we learned it in an intro class in highschool ages ago, worked pretty well there too.
- jgalt212 9mo agoC++, The Good Parts
- tialaramex 9mo agoWe should distinguish "First language" classes (for Computer Scientists who will likely learn many other languages and are expected to graduate knowing enough to just pick up another language with self study in reasonable time) from "Only language" classes for subjects where you might find it useful to write some software. These have different goals, it wouldn't make sense to teach say, OCaml as the only language but it's entirely reasonable as a first language.
- pjmlp 9mo agoBack in the 1990's, C++ used to be taught at high school students and first year university students.
- maccard 9mo agoI just went and checked my university - they’re still teaching c++ to first year uni students in 2025
- xboxnolifes 9mo agoIt's very simple. Large systems start as small systems.
- dragonwriter 9mo agoLarge systems are often aggregates of small systems, too.
- oivey 9mo agoIt’s a nice and productive language. Why is that incomprehensible?
- hibikir 9mo agoSmall startups end up writing code in whatever gets things working faster, because having too large a codebase with too much load is a champagne problem. If I told you that we were going to be running a very large payments system, with customers from startups to Amazon, you'd not write it in ruby and put the data in MongoDB, and then using its oplog as a queue... but that's what Stripe looked like. They even hired a compiler team to add type checking to the language, as that made far more sense than porting a giant monorepo to something else.
- tjwebbnorfolk 9mo agoMost large things begin life as small things.
- wiseowise 9mo agoPython has types, now even gradual static typing if you want to go further. It's irrelevant whether language is interpreted scripting if it solves your problem.
- IshKebab 9mo agoSomeone says "let's write a prototype in Python" and someone else says "are you sure we shouldn't use a a better language that is just as productive but isn't going to lock us into abysmal performance down the line?" but everyone else says "nah we don't need to worry about performance yet, and anyway it's just a prototype - we'll write a proper version when we need to"... 10 years later "ok it's too slow; our options are a) spend $10m more on servers, b) spend $5m writing a faster Python runtime before giving up later because nobody uses it, c) spend 2 years rewriting it and probably failing, during which time we can make no new features. a) it is then."
- gcanyon 9mo agoWhat language is “just as productive but isn't going to lock us into abysmal performance down the line”? What makes that language not strictly superior to Python?
- nazgul17 9mo agoLoose typing makes you really fast at writing code, as long as you can keep all the details in your head. Python is great for smaller stuff. But crossed some threshold, the lack of a mechanism that has your back starts slowing you down.
- gcanyon 9mo agoSure, my language of choice is more flexible than that: I can type put "test abc999 this" into x add 1 to char 4 to 6 of word 2 of x put x -- puts "test abc1000 this" But I'm still curious -- what's the better language?
- IshKebab 9mo agoTypescript, C#, Go, Rust. I'd say they are almost strictly superior to Python, but there are some minor factors why you might still choose Python over those. E.g. arbitrary precision integers, or the REPL. Go is a bit tedious and Rust is harder to learn (but productive once you have). But overall they would all be a better choice than Python. Yes even for startups who need to move fast.
- oofbey 9mo agoI think both points are fair. Python is slow - you should avoid it if speed is critical, but sometimes you can’t easily avoid it. I think the list itself is super long winded and not very informative. A lot of operations take about the same amount of time. Does it matter that adding two ints is very slightly slower than adding two floats? (If you even believe this is true, which I don’t.) No. A better summary would say “all of these things take about the same amount of time: simple math, function calls, etc. these things are much slower: IO.” And in that form the summary is pretty obvious.
- microtonal 9mo agoI think the list itself is super long winded and not very informative. I agree. I have to complement the author for the effort put in. However it misses the point of the original Latency numbers every programmer should know, which is to build an intuition for making good ballpark estimations of the latency of operations and that e.g. A is two orders of magnitude more expensive than B.
- i_am_a_peasant 9mo agoour build system is written in python, and i’d like it not to suck but still stay in python, so these numbers very much matter.
- Scubabear68 9mo agoNo. Python’s issue is that it is incredibly slow in use cases that surprise average developers. It is incredibly slow at very basic stuff, like calling a function or accessing a dictionary. If Python didn’t have such an enormous number of popular C and C++ based libraries it would not be here. It was saved by Numpy etc etc.
- dnautics 9mo agoi hate python but if your bottleneck is that sqlite query, optimizing a handful of addition operations is a wash. thats why you need to at least have a feel for these tables
- aragilar 9mo agoI'm not sure how Python can be described as "saved" by numpy et al., when the numerical Python ecosystem was there near the beginning, and the language and ecosystem have co-evolved? Why didn't Perl (with PDL), R or Ruby (or even php) succeed in the same way?
- HenriTEL 9mo ago22ns for a function call and dictionary key lookup, that's actually surprisingly fast.
- mrguyorama 9mo agoIn that time the java app parsed 50 strings for object hierarchies (using a regex that isn't cached) and extracted values from a request object to a processing object, handled errors, and logged results. 3 times. This is the naive version of that code, because "I will parallelize it later" and I was just getting the logic down. Turns out, when you use programming languages that are fit for purpose, you don't have to obsess over every function call, because computers are fast. I think people vastly underestimate how slow python is. We are rebuilding an internal service in Java, going from python, and our half assed first attempts are over ten times faster, no engineering required, exactly because python takes forever just to call a function. The python version was dead, and would never get any faster without radical rebuilds and massive changes anyway. It takes python 19ns to add two integers. Your CPU does it in about 0.3 ns..... in 2004. That those ints take 28 bytes each to hold in memory is probably why the new Java version of the service takes 1/10th the memory as well.
- NoteyComplexity 9mo agoAgreed, and on top of that: I think these kind of numbers are everywhere and not just specific to Python. In zig, I sometimes take a brief look to the amount of cpu cycles of various operations to avoid the amount of cache misses. While I need to aware of the alignment and the size of the data type to debloat a data structure. If their logic applies, too bad, I should quit programming since all languages have their own latency on certain operations we should aware of. There are reasons to not use Python, but that particular reason is not the one.
- notepad0x90 9mo agoFor some of these, there are alternative modules you can use, so it is important to know this. But if it really matters, I would think you'd know this already? For me, it will help with selecting what language is best for a task. I think it won't change my view that python is an excellent language to prototype in though.
- saagarjha 9mo agoI do performance optimization for a system written in Python. Most of these numbers are useless to me, because they’re completely irrelevant until they become a problem, then I measure them myself. If you are writing your code trying to save on method calls, you’re not getting any benefit from using the language and probably should pick something else.
- srean 9mo agoIt's always a balance. Good designs do not happen in a vacuum but informed with knowledge of at least the outlines of the environment. One can have a breakfast pursuing an idea -- let me spill some sticky milk on the dining table, who cares, I will clean up if it becomes a problem later. Another is, it's not much of an overbearing constraint not to make a mess with spilt milk in the first place, maybe it will not be a big bother later, but it's not hurting me much now, to be not be sloppy, so let me be a little hygienic. There's a balance between making a mess and cleaning up and not making a mess in the first place. The other extreme is to be so defensive about the possibility of creating a mess that it paralyses progress. The sweet spot is somewhere between the extremes and having the ball-park numbers in the back of one's mind helps with that. It informs about the environment.
- TacticalCoder 9mo ago> ... a function O(10_000) times in a hot loop O(10_000) is a really weird notation.
- tialaramex 9mo agoGenerously we could say they probably mean ~10_000 rather than O(10_000)
- thundergolfer 9mo agoI meant it as an order-of-magnitude notation, so means more like 10,000-90,000. Eg. calling the function 3,000 times is OK, but 30,000 is too much. Odd notation, yes, but I've picked it up somewhere along the way.
- oofbey 9mo agoI think it follows naturally from speech. People say "order ten thousand" pretty naturally. Big-O notation is often vocalized as "order". But technically it's a a clash of ideas when written that way.