Cython Tutorial - Bridging between Python and C/C++ for performance gains

what's going on everybody and welcome to a site on introduction tutorial we've got a lot of things to cover I'm going to try to get everything fit into one single video so let's get to it so first of all what is scythe on so I thought is a superset of the Python language so what this basically means is it's going to act as a bridge between Python and C / C++ and this means we're going to go both ways we can go from Python to C C++ or C++ back to Python and a lot of times we're going to do this all in one fell swoop now the glory of site ton is you can do this without really knowing anything about C C++ it's just going to generate that code for you now why would you want to do this well there's quite a few reasons like there's some kind of objects and like classes and attributes stuff like that that are just going to be more beneficial if we did it and C but actually some of the main gains you're going to see or just from typing information and that's it so cases are if you've been programming Python long enough and you've been doing things in Python you might have heard something like I've heard where it's like hey syntax why are you using Python for machine learning when you could use C or C++ and it would be so much faster well that's because I'm actually not just using Python I'm using Python and which is have just so happens to be wrapping C or C++ right that's what we do so a lot of libraries are actually C optimized libraries like numpy pandas these are c optimized libraries they just happen to have basically a python api for you so in most most cases you can actually find but already made c optimized library for whatever you're trying to do but many times you can't how or at least sometimes you can't so one way that you can it still improve the speed of your Python program is to use something like scythe on so the the main thing that at least at the very basic level that you can very simply do a scythe on there's a lot of really advanced stuff that you can do size on as well but the basic thing that you can do is just add typing information so python is a dynamically typed programming language what that means is when you type in a variable you just say x equals five but later on X could equal Gary and you're not going to have any you know at least you're not gonna have any super errors relating to at one point it was a integer and now it's a string you might have other errors in your code because of that but because it's a dynamically typed language the variable we don't have to actually tell the programming language hey this is going to be an integer or this is going to be a float the problem is every time that variable is referenced python has to say wait hold on a second let's see is this an INT is this a full stream okay okay here it is yeah it's definitely a string right this takes time now if you're only doing this once or something in a whole program you don't really have to add typing information but when you start to scale out the usage of variables either in for loops or maybe you're just a very large website that has a ton of traffic and you're scaling just in that way adding typing information can help you so much so that's what we're going to be showing here so anyways to get seith on what you're going to need is first of all you're going to need to where why are you doing this to me right now there we go so pip install or pip 3 install scythe on now I already have it although this might try to put it to Python 2 yeah anyway pip install scythe on this is actually a Python 3 tutorials so actually I would do three install size on anyway yeah I already have it the other thing you need is a compiler or C compiler so if you're on Linux you already have one yay GCC should be already here if you're on Mac it should be like Apple's Xcode I think you can grab and that has GCC I don't know much about Mac's so if you're on a Mac and that doesn't work for you sorry go to scythe ons website though and they have like a bunch of blurbs on there if you're on Windows you can use mingw that's probably the easiest one to use but it's still a pain in the butt that's why I'm filming this on a butsu anyway but yeah it can be done it's just a massive pain so anyway once you have sight on once you have a compiler you're ready to rumble so what I'm going to do is make a new folder I'm going to call it sites on tutorials and we're going to go ahead go on in there and the first thing that we're going to do is let's just let me just show us to a new document example underscore PI dot pi and let me just open this so what I mean by like static and dynamic type variables it's like in Python you could say x equals 5 right but in other languages you might have like int x equals 5 now what's icons going to expect of us is either see def is x equals whatever or not or it can be like see PDF can't x equals 5 something like that now I'll talk a little bit more about those when we get there but that's kind of what it is like so this is dynamic right X actually doesn't have to be an integer like later on like I was saying before we could say X is actually Gary screw this autocomplete anyway um cool so now let's go ahead and example pie let's do define tests tests will take one parameter that will be X and mental retains y equals zero for now and then we're going to stay cool on in whole range of X : y plus equals I and then we're going to return Y we also could say Y plus equal never mind anyway that's good enough we'll go ahead and say that and that's our regular Python program now what if we wanted to compile is with scythe on we haven't added any typing information or anything like that but any time we do do that we have to compile it to Saipan so first let me show you just how simple it is to compile to cycle so and create like a shared object and all that so first let's go ahead and go to file save as example sigh dot pi X so dot py x that's it save it done so now what we need to do is create the setup PI so let's go ahead and new document setup sup PI let's open that in sublime and now we're going to do is from this utils core imports setup just like a typical stuffs up high and then what we're going to say is from scythe on bill that's capital C capital B import scythe on eyes not typical so now we're going to say is setup and then the extension modules that we're going to be using EXT underscore modules is equal to syphon eyes and then whatever our actual pyx file is so that's going to be example dot on earth rather example size dot d Y X and that's it for the setup pipe so really there's other things we can pass in here but just for super simple purposes this is really it that's all you got to do so now all we have to do is actually run this so we'll open in terminal bring this over here can I do this you know can I do this I'd like to zoom in I know there's a command for it sorry anyway hopefully this is a simple enough anyway so python 3 set up high build underscore ext - - in place we wish I could make that bigger you can go ahead and run that let's see if it could control put I tried ctrl + it must be because I'm in a virtual machine cool anyway we'll run that looks great bunch of stuff we don't understand but that's ok the thing that we care about is right here so it's this this s oh this shared object so what's created for us is our C file some build information in here but we don't really worry about that and but actually what we care about is right here this is actual examples sign now what we could do now is new folder I call this step for deprecated and then I'm going to take example sigh what toss it in debt I didn't mean to go into death as well anyway now what we can do is we can go and do new document testing dot hi Wow got a little excited there anyway and now what we can do is we can import example underscore sign now again I moved example signup pyx just so you can see that it doesn't import that file but it won't if you had that file locally it's still not going to import it like dot pyx is not going to get imported I hope I'm not mistaken on that but pretty sure right example underscore side dot test five so save that we'll come over here and Python 3 testing dot PI is it not oh it doesn't won't print it that doesn't matter anyway it ran that's all that matters I don't want to print it out right now we will get to some more output information later anyway that's how simple it is to at least build and all that with sight on right so now all we have to do is add typing information you don't have to you can add as much or as little typing information as you want okay so it's really up to you how deep down the rabbit hole of scythe on you want to go so let's start slowly going down the hole now I put the declarations in fact I think I'm just going to pull it out because I don't really feel like that way to type them all out you can go to Python program internet to get all these as well but I'll just pull this over cool so these are just your declaration so if you've got integers hopefully you can see that well here we go so if you have an integer you can it's just see that int characters car float double right single precision double precision list Dix objects okay and then you've got def CDF and CP def for like your actual functions def it's just a regular Python function it's in Python only can't be referenced within C you've got C deaths this is a pure C function and then you've got CP def which is C in Python so it goes both ways so a common question is um you know since basically because what CP that's going to do is also generate a way to do it in Python for you whereas C death is only in scythe on so you could only reference that internally you wouldn't be able to reference that in any of your Python so then some people might ask like okay why don't we always just use CP def right well there might be some things of see that you just can't do in Python so you have to do see death okay so it's there if you need it I've never done anything because I don't know enough about C I've never done anything that I needed to use G def I've just always use CP def but if you're like real talented and C and you know a lot of tricks to the trade see def you might use but not me so anyway there's that so so those are the various declarations that we can use so now we can do is go back to example scipy YX and what are all the things that we can do here so one thing that we can do is like X we know X is going well we're going to we're going to enforce that X is going to be can't twice so int X so in the parameters you don't have to do seed of CP def you don't do anything like that really you're doing it right here so death in this case is going to just simply be a Python function but we can make it C PDF if we want to we can also specify what the return is going to be in our case it's going to be an int so this is kind of confusing so normally I wouldn't necessarily cover that immediately so first of all just we'll leave this alone let's just give typing information to X well that's possible and hopefully by the end I'll come back and throw that in there but then we're going to come down here Y so Y again is just going to be in can't so we're going to do we're going to say see death why because um so I guess I'll just go ahead and contradict myself but in there's really no reason to what we won't ever need to access Y again so we can just use C def here so I guess probably what I should the way I should have said it is my functions like the actual functions up here I would never use most likely see dev I don't think I've ever actually defined a whole function at CF but anyway that's what I was thinking when I was going through it I'm sorry anyway see def why because we're not going to access Y anywhere but this function also I so this is just think this can get kind of tricky but yet you want to pay attention to really all of the variables so in this case I is a variable and believe it or not Python is going to ask every single time we hit this I bar and here as well what's the type of I well we can help it and we can say see this int I and we forgot to give into one here so anyway I was too busy explaining why I just kind of true to myself so see deaf int I and we don't have to give it a starting value there's no no point so there's that then you've got I eyes already been defined X has already been or rather I already has a type X already has a type why are the other type I has a type Y has a type now now that we're at the end though Y is actually the return so instead what I'm going to say is see PDF in because we return an int so aunt is like what's the value of the function so that's why you've got int coming up here because this function is returning an int kind of like this bat this variable right isn't so right before the function and you give what it's going to return you don't have to do this by the way we could just use def it would be totally fine anyway CP def int test into X yeah I think this is all good so we can save that and we really just moved to run setup PI again hopefully we'll get away with that yes and then we can test it again okay but that's relatively um not exciting right now so what we're going to do now is come back over to testing and let's go ahead and let's import Tyne it will say sine equals time it dot climate assignment and we're going to run I think we can do just one line so we're going to say example underscore owes its I dot or example side dot test let's say five and then this means a set up so we'll say set up equals and this will be import example sigh kind of running off the screen hopefully I can get this to fit cool and then we're going to say PI it will we need one more variable here let's do a number equals 100 and then what we're going to do is go ahead and take this line copy paste we're going to call this now PI and example PI import example underscore PI cool all right so those are the values so none of those print let's print psych on opine for the x so basically what this does if you don't know what time it does I do have a tutorial that you can go python permanet search time it and you'll get a brief tutorial on it it just times how long these take to to go and you can do like whole chunks of them set up we'll just import it first so we don't calculate how long did the import take and it's just a really handy thing to actually time operations because these operations are really really fast and tiny changes in what's going on just in the background on your computer kind of seriously effect if you just use like import time to time these operations and probably number 100 is too low as well but anyway let's just test it so print and let's say Saipan is and it will be some variable X faster and then we'll say dot format at what spy out of sign so let's do [Music] pi / yeah basically how many times a psyphon go into Python sorry my brain is I think that's right anyway now so now we're going to go ahead and do is just run this in the terminal so come over here and now let's run Python 3 testing dot pi for 10 minutes up let's go over here where did we say - oh right here time it try again cool so in this case we can I mean this is a little hard to read but we've got the multiplier here and so we see saikhan is actually 8 times faster around one more time this can still vary yeah 12 times faster now eight times right so because let's go ahead and do let's look at thousand maybe ten thousand hopefully we can run that pretty quickly oh my god still a huge variance okay somewhere between five and fifteen times faster anyway bottom line is it's clearly faster like we haven't actually been slower so that's not too bad now what I like to do is is try to drive home why is it faster though so coming back to here here where's the the largest gain being made so for example what if we said you know if we didn't do this like what if we just got rid of I here and is just remove that save and then now let's just rebuild retest and then hmm that's um not much faster now it's actually slower whoops oh shoot what did I do I think I rebuilt it there we go anyway slower a little faster little faster slower slower right so just that line made a huge difference right what if okay so clearly into eye matters what about what oh I'm not appreciate commenting should work it yeah there's no reason why that won't work but I'm just going to leave it anyways let's rebuild test it again Oh exception why reference before oh yeah what a noob try again there we go so um so now it's like three four nine three four four four four okay so clearly that one also matters right that made a big difference okay trying to think of what else we could do we could we could take away the typing information for X now this should be checked only once right it'll it'll go through a range but it should only be checked once so I'm going to wager that's not going to have a huge impact but let's see so we can build let's test right test test test right not a big impact because it was only referenced one time okay tracked I think we're all set on all the other variables at this point so so that wasn't really truly necessary so what I'm trying to point to though is that the huge gain happened basically everything that was involved in this for loop because every time we go through it we've got to reference that variable except for X because X is only value X isn't being reassessed every single time we go through this loop how do I know that because we didn't gain games by you know not chain you know like like object we all need the reference value of X once before we know okay how many loops or interations are we going to do we don't need to read you know keep rear-ending what is X what is X that's not that we don't have to do that so anyway okay so that's one thing now knowing what we know in this loop so you know maybe you want to impress all your friends who aren't Python programmers and you want to say this is why I use Python and I know how to make Python so fast so what's one way that we could make this better because a lot of times you know maybe you've heard that scythe on can help you be like 200 times faster right so what could we do well we could just make that that four leaf larger so like what if we said rather than five what if we said 5000 we might have to change this number of iterations let's do a thousand save we don't need to rebuild we just test again boom 119 times faster they're out 36 that's ugly let's go back to get one 1801 24 okay so we're pretty we're pretty ballin at this point on stripe 50,000 Oh taking forever come on it's going to be faster Wow I think we went down in speed 140 times we're going with that one okay so we've written code that's 140 times faster anyway okay so there are at least a few examples or at least one example of some simple code but adding some simple typing information which ones actually mattered which ones really didn't matter for example two let's get rid of the definition here so let's just take away that entire top line again this shouldn't have really a huge effect I hope I'm not wrong but Python 3 testing dot pi obvious we left our loop gigantic but anyway cool yeah so but they're going to have like a huge impact in before like 36 yeah cool so so that's not really essential that you give it this the only time I may be essential really prime in my opinion is if it needed to be a seed if but anyway or if you're calling the function whole bunch of times in a loop make it CP desc give the return of it and then give this of okay now let me go ahead and build that one more time let's test it and I want to show one more thing for I let you all go and that is the the HTML kind of conversion that you can get from this so so what I'd like to do is let's take and try and set how I want to do this because we can't let's go to example dot pi so let's copy this paste so weird is pasting the original example dot PI into the new example side out pyx kind of what we had initially I saved it and then now I'm going to do is go into the terminal and I am going to do I think it's just Saipan - a and then let's call this what was the example it's just example underscore Sun vample underscore its size dot p YX will run that and what this does is it just creates your C file and ah even though this is here it doesn't create your s o file I don't know why I wish if it was a single file you could just do size on a rather and have the setup PI or some form of saipan if somebody knows that you can do that without setup pi let me know because it doesn't make any sense like why wouldn't you just be able to build it with just the size on call but for whatever reason you can but what I'm interested in is the HTML file it produces so what we can do is we can open this in Firefox and basically as it tells you right here the yellow lines hint at your Python interaction interestingly enough y equals zero apparently isn't super close I think it's there it's just the least interactive to Python but anyway you can see all of you know how close are we in in Python so clearly the definition is just pure Python and then the for loop is very heavy in Python so now we can close this and let's go back here let's just do ctrl Z save and then let's now do the same thing again we'll get a new HTML file let's open that one and now we get basically only one line that's the first line which is CP def because we wanted to be able to reference it and use it in Python but other than that the rest of this is nowhere near Python okay so anyway pretty cool so so what has it done for you basically like this for loop has been written for you in C so that's in this file here and I don't know about you but I'm not going to write like especially if you have like a large Python program I mean it's going to generate like yeah like let's say 50 lines of Python then generate like hundreds of lines in C for you which would be very annoying to to write yourself and I probably would not be successful but obviously this is it's pretty successful super tested I like I said before it's used in a lot of large libraries like numpy pandas um's and so on it's a huge list of packages that use scythe on okay I think that we've made it through everything I wanted to cover at the the most basic level hopefully that was simple enough I personally was really surprised I had looked into scythe on quite a few times in the past and I just kind of found the documentation to be not so great I found a lot of kind of like tutorials on Saipan but it was really like talks on Saipan without actually showing exactly the code and so for the longest time I just couldn't figure out Saipan but then when I figured it out and I realized oh my gosh it's basically at least a beginner insight on all it is just typing information that's it there are more interesting things that you can do obviously if you're C programmer or C++ there's some other things you should look into also we can't do it in this for loop but there are certain things that we can add with like with no guild so this will release the Gil for you you can do things unfortunately you're not going to be able to do this you're not going to be able to modify this without the Gil obviously you couldn't do that and see anyways like you couldn't you'd have to handle for that but there's some things that you can do without the Gil as long as they're not you know changing some sort of shared variable or something like that but yeah there's there's quite a few other things that we can do with scythe on and I might cover them more in the future but at even the most basic level just adding typing information can give you huge improvements so anyways that's all for now if you have questions comments concerns something specific you'd like me to cover in scythe on feel free to let me know below otherwise as always thanks for watching things for all those for subscriptions and I will see you in another video

Channel: sentdex

Views: 236,993

Rating: 4.8736944 out of 5

Keywords: cython, python, C++, c programming, programming, tutorial

Id: mXuEoqK4bEc

Length: 29min 41sec (1781 seconds)

Published: Mon Jul 10 2017