Episode: 539
Title: HPR0539: Little Bit of Python Episode 7
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr0539/hpr0539.mp3
Transcribed: 2025-10-07 22:43:32

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Welcome to a little bit of Python, episode 7 on Unladen Swallow with Brett Cannon, Steve
Holden, Jesse Naller, Michael Ford, and myself Andrew Kushling.
So should we cover real fast what Unladen Swallow is?
Yes, we should.
Unladen Swallow is a branch which started out as I believe a branch of the 2.6 code may have
been the 2.5 code and what they're trying to do is to introduce selective speed ups into the
interpreter. So with it be the idea behind making it a branch was that it should be relatively
easy to integrate and the original intention was to integrate it back into the Python 2 series.
So what they're doing is they're adopting just entire compiler technology and I think they're
targeting the LLVM virtual machine which is a virtual machine that's previously been used for
other language systems in which has I understand just arrived at the stage where the LLVM
compiler can compile itself now. It was something I seem to remember reading this week but
they were all right okay that was an LLVM based project I beg your pardon but anyway it's
technology that's currently actively being worked on and the interesting thing is that
the Unladen Swallow developers who's worked by the way has already been used inside Google
because most of the original team were Googlers I think it was Thomas Faltes and Colin Winter wasn't it?
So they're already putting the code into practical engineering using Google but they are now
proposing to merge the results into Python 3 which has resulted in some very active conversations.
It's very active so yeah the original team was Thomas Wooters, Colin Winter, Jeffrey Askin and
then they've added a few people read who I believe is an LLVM maintainer if I'm not mistaken.
So the team has definitely grown and like Steve said, Unladen Swallow made a bit of a splash
at last year's Picon in 2009 by basically walking into the virtual machine summit and saying
we have branched Python 2.6 and YouTube is now using it. So it's been in production use
often on inside of Google for some time and if you check the mailing list archives for Unladen Swallow
you can see the other people and companies have actually been putting it to actual use
since the project is started. Now some people's response to Unladen Python Unladen Swallow has been
to treat it like snarek oil I think would be a fair summary because they've seen early results
where the I suppose the execution time benchmarks have been shall we say indecisive although certain
benchmarks have definitely reported speed up but I think some people have focused on the much
larger memory requirements of the interpreters using the branch code. When the Unladen Swallow guys
started and they announced that they were integrating a just in time compiler into Python which
is very sexy technology and everyone wants a just in time compiler into in Python and they said
our goal is to get Python five times faster and then I think they found that the the LLV
and the parts of the LLVN that they were using were actually parts that weren't much although the LLVN
is is used massively it's used by Apple and their Apple sponsored developments of a lot of it.
Those parts weren't the parts that the LLV and Swallow guys were using weren't used quite
so well and more than as quiet as good as shape as they thought so the proposal that comes
the table with it will let's say it's not certainly not shown five times performance improvements
on most of the benchmarks so some people are quite disappointed but as I think will come out in
the conversation that the proposal that they've just that they've put on the table is very much
the start of making Python much faster it's technology that really paves the way for us getting
a much faster Python. The key thing is as Michael said it paves the way they've made sure from the
beginning that the design was such that it was extensible and easy to build on top of so a big
part of only in Swallow was to get some initial speed ups yes but also to build the foundation needed
to continue to improve the performance as time goes on and people get no ideas on how to speed
things up and add things etc etc. It really is a foundation yeah there are a few things that are
controversial about the proposal I mean the first one is that the Pat 3146 which was announced
very recently merging unlabeled swallow back into CPython so this is happening soon that's
the idea how soon is anyone's guess but the things are first of all they tell getting Python 3 and
not Python 2.6 the memory uses is a lot higher the startup time is slower the binaries are bigger
we're going to have C++ in the code base in the Python CPython code base for the first time
so it's not an controversial proposal on the other hand it is important that we bring these
issues on to the table and talk about them how much larger memory usage is unacceptable
for example or how big an improvement does there need to be for it to be worthwhile and can we
come to a consensus on that but does memory usage matter if you can turn it off I think Java's
proven memory memory usage is not a big issue for a lot of people and also I think the reaction
from Python dev has led the unlabeled swallow developers to take a second look at their code and
to find omissions so for example when you turn off the jit they realized that they were still
initializing all of the jit data structures even though they're never actually used and so the
memory usage is therefore a bit artificially high when you're not using the jit at all
and I'm sure there are going to be other minor bugs of this sort that will turn up
well and that's kind of the point of proposing it inside of the pep is to kind of scroll these
things up no one I don't think anyone involved or talking to Colin or anyone anyone at all was
under the impression this would just be a you know oh look we're going to merge it done
there's certain things there's certain requirements that have to be met I mean Colin and the rest
of the unlin swallow guys have done exactly what Andrew was saying which is oh you know we've
proposed the pep we've gotten feedback like we have to be able to completely disable this if we
don't want this and they've gone out of their way to kind of say you know we're going to go back
we're going to fix these bugs we're going to make memory usage better we're going to decrease
the binary size and a lot of these have actually been bugs so and it's also important to note that
the way the pep is structured is the first thing is going the first thing that would happen is
that they would basically be merged into the python subversion or material tree whichever comes
first and they would have their own private branch at which point more bugs would be kind of
fixed and scrolled out you know and resolved and then eventually once those bugs are fixed
and once it is met you know the high standards that python core does have it would be merged into
pie three so it's not it's not you know it's not a shoe in it's not going to happen overnight
but it's it's really setting the foundation for a much faster python in the future and also I mean
to Michael's point we will have C++ in the code base however you don't need to use it so while
it's there it's important to remember that LLVM and UnLatin Swallow work on the byte code level
so developers who want to add features to python won't actually need to work within the constraints
that UnLatin Swallow adds or work within C++ they will be able to work on the same interpreter
they know they love later on if they choose to add the optimizations in C++ inside of the UnLatin
Swallow Jit system so you're saying that it's it's actually going to be fairly effectively ring
fence as far as other developers are concerned there's farza more yes that's good the python's
API would continue to be pure C functions and C header files it's farza more yes now I could be
wrong the relationship isn't always clear but you will be able to write and add features to the
language in regular old C and then later optimize them using P++ and UnLatin Swallow's work that's
that's definitely true the only issue is that as if you're using the version of the python if
you're linking against the version of python that uses the UnLatin Swallow parts then there may be
issues around using two different C++ runtimes because that can cause issues in some projects
but by default it's not going to change the way you develop but I think there is going to be
some careful consideration about how is this going to affect C++ projects that currently embed
python who might want to embed the version that includes UnLatin Swallow and I think on a lot of
platforms that's not a problem because you'll just be able to use the same version of the C++
runtime to compile the whole thing but I think it may be an issue on some of the more obscure
platforms and it will run on Windows yeah that that was an issue a while ago the LLVM didn't project itself
didn't have many Windows developers although they they claim support for Windows it wasn't very
well tested but the UnLatin Swallow cars are said to look with the current code we've got
with all the fixes that we've pushed back into the LLVM all the changes we've made
all of the python tests and all of the UnLatin Swallow tests all part on Windows
so Windows supports with UnLatin Swallow is currently good which is good news.
On the C++ note there's actually a section inside of the pepset called the addition of C++2C
Python and it's just really briefly highlights it says ease of use of LLVM's full powerful code
generation and related APIs convenient abstract data structures to simplify code and the C++ is
limited to limited to a relatively small corner or corners of the C++ on code base and then it says
of course the low lights a C++ style guide would have to be developed and enforced and developers
must know two related languages C and C++ to work on the whole range of CPython's
internals so it is going to be sandboxed pretty well yeah it does make more demands of a developer
who wants to integrate fully with Python then doesn't it I mean it brings some interesting
questions out about just how important execution speed is I know for example there are some
people who work in the financial world where their predictive algorithms your speed is absolutely
everything and they they will quite happily expend huge amounts of money on on extremely fast software
extremely fast hardware to get the maximum amount of it obviously they're going to be quite
happy about paying for increased speed with additional memory but that's not everyone of course
and the problem that the developers have is trying to strike a compromise that's suitable for
everybody that's happening it keeps everyone happy well and that's why we have the flags to be
able to disable it right I mean it's it's being able to get it out of your way when you don't need
it is going to be just as critical having it when you do yeah I think it's important to keep
a perspective that the lean swallow speed ups are not going to be for everyone as it's obviously
been said there's memory pressure there's speed up cost I think it's going to be to do something
kind of like Java is on the server it's something for those long-running processes where over time
the amortized upfront cost is going to be completely blown away by the long-term speed up
but for stuff when you're launching like some command line to one python it's not going to be
the version you're going to want to use bingo I think there are a lot of people who do care about
python performance though and as you can tell by interest in projects like cycle and why people
are so excited by um by unleavens well I think there are a lot of people who want python to run
faster and there are projects where they don't or can't use python that they would like to use it for
sure at the same time if if the interpreter start up takes a lot longer then people who typically
run short scripts um end up paying a penalty for that but like I was saying it's it's important for
the short-lived you know one-off scripts you can just pass the flag that says don't enable the
jet but for those of us who are running on longer-running server processes this is pretty much a very
large boom for us um especially in the web app space where a lot of your processes may be extremely
long-lived and you know just dealing with network damans where you'll have something that hopefully
fingers crossed will run for maybe years and the unleavens swallow developers are aware
that there are people who care a lot about start-up time and one of the more impressive things about
their project is they've done a lot of work on benchmarking for the case of start-up they actually
have a full set of tools that they try like for example I think they're using recurrent bizarre
as tests so how how long does it take to fire up a bizarre process and print a help message
the resulting set of benchmark tools is I think going to be really useful for other applications
in future as well I it's already it's already very useful the i and python guys are just starting
to use the unleavens swallow performance benchmarking tools and the pypava guys are already
using them because a lot of the other python benchmarks that we have are all micro benchmarks
which don't tell you very much about actual application performance and the unleavens swallow
benchmarks are sort of real well this is the sort of thing you really do with your python code I
mean they're focused on the things google does with that python code which is stuff like jango
templating and and that kind of stuff but it's a decent set of real world performance benchmarks
which is a great thing to have for listeners who want more information about this I strongly suggest
going to read the pep pep number three thousand one hundred and forty six because it's a really
interesting document they talk about the original rationale for the project and their history
and how the project got deflected into fixing bugs in lvm and in improving the ability to debug
and profile jitter code and it lays out a lot of the issues being faced here this this is my
favorite bit from the pep it says we explicitly reject any suggestion that our ideas are original
we sort to reuse the published work of other researchers wherever possible if we've done any
original work it is by accident and people have said similar things about python that it's not a
research language that innovates it consolidates features i think if you're looking for that kind
of innovation then pypy is the place to go because they're really trying to do innovative new stuff
particularly on the jiffrums and it'll be nice when python has two good working fast efficient gyps
my final thoughts on that are cahn and the rest of the unlaimed swallow team have been very very
pragmatic which is you know one of the great things about the python community it's always very
pragmatic about the features we add what we do how we approach things i mean real world benchmarks
you know what can we accomplish you know what can we do rationally and you know keep things working
and i mean much like Andrew said read the pep read the discussion on python dev because it's
very very grounded in you know re solving real problems and not you know doing some sort of bizarre
architectural astronaut we're going to create something all new and all knowing it's very much grounded
in pragmatically what can we do to speed python up now i mean we've talked a lot about the the
problems with um that unlabeled swallow faces and that it's in the process of overcoming but i
think the future for it is very bright they're already showing at you know at least 50 percent
performance improvement on a lot of those those benchmarks almost twice as fast on some of them
and there's a lot of stuff that they're not doing yet they're not unboxing the primitive types
like integers and floats so i mean there's an obvious big improvements to be had when they
start looking at these kind of optimizations they're not yet doing tracing um one one possibility
that's been talked about it is taking the the jissids um cut the native code that's generated
and actually possibly being able to save that out separately as as a dll or as an so file
so that you you can um you can basically take prejudiced code and as we start to look at those
perform those sort of optimizations none of which are massively innovative they've all been
been done on other platforms so they're all well within the bounds of possibility but there's all
sorts of interesting uh things that could happen in the future if you're thinking about unlabeled
swallow i mean like we said like we said in the beginning this is a foundation for a much much
faster python they've only touched the tip of the iceberg when it comes to the optimizations they
can do and as time goes by we're just going to keep adding or they they and all of us in python
core are going to learn and we're going to keep adding optimizations it can only get faster
so i mean i guess that the the VM summits and the language summits coming up on a one of the places
this is going to be discussed in detail but do we have any idea any rough framework of the sort
of time frames we're looking at are they talking about getting it into python 3.2 or python 3.3
i don't know off the top of my head of which which exact version they're targeting the merge
pep has to be accepted and then we have to i suspect the pep's going to be accepted personally
i mean the the unlearned swallowguides have pretty much addressed most of the issues and
they've made it clear that if you compile if you compile python without the L of the jit support
it will be pure sea and that basically it's an opt-in solution and if you opt out it's not going
in any way impact your system so honestly i'm not seen as in any way negative so i suspect it
will get in it's just a question of how many people use it and who really gets into trying to add
new speed features compared to adding new language features and just how that kind of plays out but
i see it happen in personally the great thing is is we get their developers everybody everybody
involved in lln not llvm but everybody involved in the mean swallow comes to python core for free
which is you know in my in my book you know the more the merrier and the schedule for python 3.2
calls for the first beta release in september 2010 it might be a little tight but it seems
at least feasible to envision this going into python 3.2 i've talked to cologne he seems pretty
positive that it will actually happen i mean i think the guys get to spend time to do it
as their job at google once it gets accepted so i think they're going to start fairly soon and
they should actually be able to get it done i think i have faith great so the future is bright
this has been a little bit of python episode 7 with brachanan michael ford
steve holden jessie naller and myself andru kushling please send your comments and suggestions
to the email address all at bit of python.com our theme is track 11 from the headroom project
is known python available on the magnitude label
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