LPython: Novel, Fast, Retargetable Python Compiler(lpython.org)
lpython.org
LPython: Novel, Fast, Retargetable Python Compiler
https://lpython.org/blog/2023/07/lpython-novel-fast-retargetable-python-compiler/
100 comments
We put this sentence there to drive the point home that LPython competes with C++, C and Fortran in terms of speed. The internals are shared with LFortran, and LFortran competes with all other Fortran compilers, that traditionally are often faster than C++ for numerical code. I've been using Python for over 20 years and it's hard for me to imagine that writing Python could actually be faster than Clang/C++, somehow I always think that Python is slow. Right now we are still alpha and sometimes we are slower than C++. Once we reach beta, if an equivalent C++ or Fortran code is faster than LPython, then it should be a bug to report.
What happens when including numba or pytorch, etc in the scripts? GPU acceleration in python is one really nice way of getting decent speed, but I would imagine it's difficult to shuffle over when doing this type of compiling. If the end compiled program allows for use of all available computational resources (some logic with python to determine what accelerations to allocate, what is available, etc) and then can compile to C++ speeds for CPU and use GPU where appropriate, this will be astoundingly good.
Right we support (currently a subset) of NumPy (just `from numpy import ...`) and SymPy (`from sympy import ...`) and some parts of the Python standard library. We want to support PyTorch, CuPy and other such libraries in a similar way, at least the subset that can be ahead of time compiled, which is quite large.
Yes, offloading to GPU we want to support naturally via NumPy syntax. We will look at this very soon, most likely via annotating that a given array lives on a GPU or host, and then array copy will copy it from host to device, etc.
Yes, offloading to GPU we want to support naturally via NumPy syntax. We will look at this very soon, most likely via annotating that a given array lives on a GPU or host, and then array copy will copy it from host to device, etc.
I thought that Fortran was traditionally faster than C++ for numerical code due to stricter aliasing rules in the language, which I wouldn't expect to carry over to an IR?
That, but also being simpler and higher level, having multidimensional arrays in the language itself and simpler semantics (such as you cannot just take a pointer to an arbitrary variable, it has to be marked with "target"), no exceptions, and so on. What carries over to the IR today are all the language semantic features, such as all the array operations (minloc, maxval, sum, ...) and functions (sin, cos, special functions) as well as all the other features without any lowering, and we then do optimizations at this high level, then only at the end we lower (say to LLVM). Python/NumPy can be optimized in exactly the same way, and that's what LPython does. I think C++ can also be compiled this way, but the frontend would have to understand basic structures like `std::vector`, `std::unordered_map` as well as arrays (say xtensor or Kokkos, whatever library you use for arrays), and lift it to our high level IR. Possibly we would have to restrict some C++ features if they impeded with performance, such as exceptions --- I am not an expert on C++ compilers, I am only a user of C++.
Nuitka is just a packaging system which places all dependencies inside of an executable. It doesn't compile into machine code. Why do you conflate it with compilers?
It is absolutely a compiler. I've certainly spent enough time waiting for it to compile! On the contrary, packing dependencies is a side effect rather than its primary purpose. (Your sarcastic last sentence doesn't help your point, even if you weren't wrong.)
However, it really is different from projects like this one, in that it doesn't attempt to obtain C-like speed (but does hope to do some optimisations). For example, x+=1 will still dynamically dispatch depending on the runtime type of x, and (if it's an int) do the normal Python arbitrary precision operation. But those will be called from machine code rather than interpreted byte code.
(Essentially, it unrolls the main loop of the CPython interpreter, which is written in C, for every byte code operation, and eliminates every case of the switch statement inside except the one that corresponds to this operation. That's what gets compiled.)
However, it really is different from projects like this one, in that it doesn't attempt to obtain C-like speed (but does hope to do some optimisations). For example, x+=1 will still dynamically dispatch depending on the runtime type of x, and (if it's an int) do the normal Python arbitrary precision operation. But those will be called from machine code rather than interpreted byte code.
(Essentially, it unrolls the main loop of the CPython interpreter, which is written in C, for every byte code operation, and eliminates every case of the switch statement inside except the one that corresponds to this operation. That's what gets compiled.)
Just to be clear, the reason I didn't (and won't) accept nuitka as a compiler is that it doesn't do what actual compilers do, it just plays around with bytecode. I experienced no speed difference when running large programs, but the startup is considerably slower. To me, it is just a docker replacement that is 1/10th as portable.
A compiler doesn't need to optimize. I think if it takes Python code, and translates it to something else, it's a compiler. An optimizing compiler is the one that will give you speedups.
And Nuitka does optimize: https://nuitka.net/doc/user-manual.html#optimization
Then it's an optimizing compiler for sure.
"plays around with bytecode"?
Even if that is so, it translates the whole program to c++, which is then compiled. It relies on libpython to implement a lot of the core language types and such, so if your program isn't very computationally intensive or makes heavy use of core data types, you might not notice much, but it's definitely a compiler.
Since you're commenting from opiniated ignorance, you might want to read the Nuitka page itself:
> Nuitka is the Python compiler. ... It then executes uncompiled code and compiled code together in an extremely compatible manner. Nuitka translates the Python modules into a C level program that then uses libpython and static C files of its own to execute in the same way as CPython does.
I'm happy to stick by the tool's own description of itself. But if you don't accept that, and Nuitka still isn't a compiler by you, sure. Go ahead with your pedantic and strictest definition of the meaning of a 'compiler'.
Learn to read English, before insisting on your pedantry as some sort of truth, in disregard of the tool's own intent/description. (And I do hope you take issue with everyone's description of Typescript as a compiled programming language too.)
> Nuitka is the Python compiler. ... It then executes uncompiled code and compiled code together in an extremely compatible manner. Nuitka translates the Python modules into a C level program that then uses libpython and static C files of its own to execute in the same way as CPython does.
I'm happy to stick by the tool's own description of itself. But if you don't accept that, and Nuitka still isn't a compiler by you, sure. Go ahead with your pedantic and strictest definition of the meaning of a 'compiler'.
Learn to read English, before insisting on your pedantry as some sort of truth, in disregard of the tool's own intent/description. (And I do hope you take issue with everyone's description of Typescript as a compiled programming language too.)
Let's be reasonable: Nuitka's sales pitch really isn't really a good source of information. And be aware that it doesn't say the code is converted or compiled to C. It just says it loads python code from C and runs it on the interpreter, which is basically what the python interpreter does.
I think my comment being devoid of content might have caused some frustration. So to make the best of everyone's time:
You can look into cython and pythran to see what I'm talking about. cython lets you optimize code step by step via generating an html page with your code and highlighting lines that still require the use of the python runtime. It lets you add types and cdef function definitions in order to reduce your dependency on the python runtime.
Another good example is pythran, which takes your python code and turns it into c++ code to be compiled by a c++ compiler. I understand that this isn't a direct compilation to machine code, but a middle step which lets you compile the output to machine code.
Then there is numba and taichi which have just-in-time compilation decorators. Taichi also provides a sophisticated runtime which lets you run parts of the code on a GPU.
Surprisingly, the best performance I've experienced among these examples was numba + numpy, even though numba alone can sometimes have optimizations that surpasses all compilation efforts, because it turns your loops into mathematical formulas and runs them at O(1) complexity when it can.
I think my comment being devoid of content might have caused some frustration. So to make the best of everyone's time:
You can look into cython and pythran to see what I'm talking about. cython lets you optimize code step by step via generating an html page with your code and highlighting lines that still require the use of the python runtime. It lets you add types and cdef function definitions in order to reduce your dependency on the python runtime.
Another good example is pythran, which takes your python code and turns it into c++ code to be compiled by a c++ compiler. I understand that this isn't a direct compilation to machine code, but a middle step which lets you compile the output to machine code.
Then there is numba and taichi which have just-in-time compilation decorators. Taichi also provides a sophisticated runtime which lets you run parts of the code on a GPU.
Surprisingly, the best performance I've experienced among these examples was numba + numpy, even though numba alone can sometimes have optimizations that surpasses all compilation efforts, because it turns your loops into mathematical formulas and runs them at O(1) complexity when it can.
Nuitka is a compiler. With list it at the bottom of https://lpython.org/, together with the other 23 Python compilers, now 24. :)
Looks very interesting indeed.
Two questions come to my mind:
- presumably, since it is compiled, it does static checks on the code? How many statically-detectable bugs that are now purely triggered at runtime can be eliminated with LPython?
- does it deal with the unholy amounts of dynamism of Python? Can you call getattr, setattr on random objects? Does eval work? Etc. Quite a few Python packages use these at least once somewhere...
Two questions come to my mind:
- presumably, since it is compiled, it does static checks on the code? How many statically-detectable bugs that are now purely triggered at runtime can be eliminated with LPython?
- does it deal with the unholy amounts of dynamism of Python? Can you call getattr, setattr on random objects? Does eval work? Etc. Quite a few Python packages use these at least once somewhere...
> - presumably, since it is compiled, it does static checks on the code? How many statically-detectable bugs that are now purely triggered at runtime can be eliminated with LPython?
Yes, it does static checks at compile time. The only thing that we do at runtime (imperfectly right now, eventually perfectly) are array/list bounds checks, integer overflow during arithmetic or casting and such. Those checks would only run in Debug and ReleaseSafe modes, but not in Release mode. So for full performance, you choose the Release mode. For 100% safe mode, you would need to use ReleaseFast.
- does it deal with the unholy amounts of dynamism of Python? Can you call getattr, setattr on random objects? Does eval work? Etc. Quite a few Python packages use these at least once somewhere...
It deals with it by not allowing it. We will support as much as we can, as long as it can be robustly ahead of time compiled to high performance code. The rest you can always use just via our CPython "escape hatch". The idea is that either you want performance (then restrict to the subset that can be compiled to high performance code) or you don't (then just use CPython).
Yes, it does static checks at compile time. The only thing that we do at runtime (imperfectly right now, eventually perfectly) are array/list bounds checks, integer overflow during arithmetic or casting and such. Those checks would only run in Debug and ReleaseSafe modes, but not in Release mode. So for full performance, you choose the Release mode. For 100% safe mode, you would need to use ReleaseFast.
- does it deal with the unholy amounts of dynamism of Python? Can you call getattr, setattr on random objects? Does eval work? Etc. Quite a few Python packages use these at least once somewhere...
It deals with it by not allowing it. We will support as much as we can, as long as it can be robustly ahead of time compiled to high performance code. The rest you can always use just via our CPython "escape hatch". The idea is that either you want performance (then restrict to the subset that can be compiled to high performance code) or you don't (then just use CPython).
For a system that doesn't intend to handle arbitrary unaltered Python code, I think a post announcing a "Python Compiler" should make this clearer in the first paragraph.
You are right, we should have made that clearer. If you look at all the 25 compilers that we list at the bottom of: https://lpython.org/, some of them are supersets, some of them are subsets. Sometimes the distinction is blurry, since even with LPython you can call arbitrary CPython today, it just doesn't get compiled right now, but perhaps later we can actually compile it like Cython does, just not speed it up much. In that case we become a subset that is fast, the rest is slower, but I think every superset of Python behaves like that too. In a way, I think all of the 25 compilers supports all of Python one way or the other (LPython as well), and I think each of them only gets a subset to be fast.
If you have some ideas how to best communicate this, let me know.
The best approach that I know right now is to say that we support a strict subset of Python, and if it compiles, it will be fast. The rest of Python you have to call explicitly and it will be slow and you get a CPython dependency in the binary that we generate, but you can do it. That way there is a clear distinction what gets compiled via our compiler into high performance machine code and what gets dispatched via CPython (it will eventually get "compiled", but it will just call CPython).
If you have some ideas how to best communicate this, let me know.
The best approach that I know right now is to say that we support a strict subset of Python, and if it compiles, it will be fast. The rest of Python you have to call explicitly and it will be slow and you get a CPython dependency in the binary that we generate, but you can do it. That way there is a clear distinction what gets compiled via our compiler into high performance machine code and what gets dispatched via CPython (it will eventually get "compiled", but it will just call CPython).
I guess I'd put it like "LPython compiles a type-annotated Python subset (dialect? variant?) to optimized machine code. Interop with CPython is easy: arbitrary Python code can go in the same source file using a decorator." -- just as an example to try to be helpful -- of course you know your system and I don't. It sounds really cool and I'm wishing you luck.
Thank you! I opened up an issue to do this: https://github.com/lcompilers/lpython/issues/2220.
I think your second point is especially important, as the semantics of Python are dynamic down to the core. And it's not just hypothetical stuff — Python libraries pretty systematically take advantage of this dynamism (anyone who's tried using type stubs for popular libraries will know what I mean).
The examples in the article appear to mainly revolve around numerical calculations, so I suspect the target audience is people doing scientific computing who need to "break out" into a compiled mode for heavy CPU calculations (similar to numba or even Julia) from time to time when their calculations aren't vectorisable.
I've noticed a split between the needs of software engineers on the one hand, who need expressive abstractions to manage systems of extensive rather than intensive complexity, and scientific programmers or model-builders on the other hand, who are much more likely to just use the primitives offered by their language or library as their needs revolve around implementing complicated algorithms.
The examples in the article appear to mainly revolve around numerical calculations, so I suspect the target audience is people doing scientific computing who need to "break out" into a compiled mode for heavy CPU calculations (similar to numba or even Julia) from time to time when their calculations aren't vectorisable.
I've noticed a split between the needs of software engineers on the one hand, who need expressive abstractions to manage systems of extensive rather than intensive complexity, and scientific programmers or model-builders on the other hand, who are much more likely to just use the primitives offered by their language or library as their needs revolve around implementing complicated algorithms.
This looks very cool ! There is also MyPyC which is not in the comparison table, but worth noting.
They have some benchmarks vs regular python here :
https://github.com/mypyc/mypyc-benchmark-results/blob/master...
One difference is that MyPyC compiles your code to a C extension, so your are still dependent on python. On the other hand you can call regular python libraries with the normal syntax while, in LPython, the "break-out" syntax to regular libraries isn't straightforward
In any case super exiting to see work going into AOT python
They have some benchmarks vs regular python here :
https://github.com/mypyc/mypyc-benchmark-results/blob/master...
One difference is that MyPyC compiles your code to a C extension, so your are still dependent on python. On the other hand you can call regular python libraries with the normal syntax while, in LPython, the "break-out" syntax to regular libraries isn't straightforward
In any case super exiting to see work going into AOT python
Awesome, thank you. I knew about mypyc, but forgot. I just put it in:
https://github.com/lcompilers/lpython.org-deploy/pull/37
So now we have 25 compilers there.
Yes, the current syntax to call CPython is low level, you have to create an explicit interface. We can later make it more straightforward, such as using a `@python` decorator to a function, where inside you just do CPython. We always want to make it explicit, since it will be slow, and by default we want the LPython code to always be fast.
https://github.com/lcompilers/lpython.org-deploy/pull/37
So now we have 25 compilers there.
Yes, the current syntax to call CPython is low level, you have to create an explicit interface. We can later make it more straightforward, such as using a `@python` decorator to a function, where inside you just do CPython. We always want to make it explicit, since it will be slow, and by default we want the LPython code to always be fast.
Nitpick: The "Documentation" button on the header links to LFortran, not LPython.
With that said, I love the fact that this can generate executables, and I'm looking forward to trying it out in the future! Python compilers are really cool. I recently used Nuitka to build a standalone version of an app I wrote for my own use, so that I can run it on hosts that don't have Python installed (or don't have the right Python packages installed yet). This seems to be focused much more on speed.
One thing which I didn't understand from the homepage: can I take vanilla Python code and AOT compile it with this?
With that said, I love the fact that this can generate executables, and I'm looking forward to trying it out in the future! Python compilers are really cool. I recently used Nuitka to build a standalone version of an app I wrote for my own use, so that I can run it on hosts that don't have Python installed (or don't have the right Python packages installed yet). This seems to be focused much more on speed.
One thing which I didn't understand from the homepage: can I take vanilla Python code and AOT compile it with this?
> Nitpick: The "Documentation" button on the header links to LFortran, not LPython.
Yes, I noticed too, thanks. We currently don't have a dedicated documentation for LPython and a lot of the LFortran documentation applies. We will eventually have a dedicated LPython documentation.
> With that said, I love the fact that this can generate executables, and I'm looking forward to trying it out in the future! Python compilers are really cool. I recently used Nuitka to build a standalone version of an app I wrote for my own use, so that I can run it on hosts that don't have Python installed (or don't have the right Python packages installed yet). This seems to be focused much more on speed.
We focus on speed, but we definitely create executables (no Python dependencies), just like any other C or Fortran compiler would. You only get a CPython dependency if you call into CPython (explicitly). Indeed creating such standalone executables simplifies the deployment and packaging issues: all the packages must be resolved at compile time, once you compile your application, there are no more dependencies on your Python packages (unless any of them calls into CPython of course).
> One thing which I didn't understand from the homepage: can I take vanilla Python code and AOT compile it with this?
Only if that vanilla Python compiles with LPython (since any LPython code is just Python code, a subset). So in general no. If you call CPython from your LPython main program (let's say), then you will get a small binary that depends on CPython to call into your Python code. I thought about somehow packaging the Python sources into the executable, similar to how PyOxidizer does it, but that's a project on its own almost. We will see what the community wants. If we can make LPython support a large enough subset of CPython, I think I would like to use LPython as is, since it's nice to not have any Python dependency and everything being high performance, essentially equivalent to writing C++ or Fortran.
Yes, I noticed too, thanks. We currently don't have a dedicated documentation for LPython and a lot of the LFortran documentation applies. We will eventually have a dedicated LPython documentation.
> With that said, I love the fact that this can generate executables, and I'm looking forward to trying it out in the future! Python compilers are really cool. I recently used Nuitka to build a standalone version of an app I wrote for my own use, so that I can run it on hosts that don't have Python installed (or don't have the right Python packages installed yet). This seems to be focused much more on speed.
We focus on speed, but we definitely create executables (no Python dependencies), just like any other C or Fortran compiler would. You only get a CPython dependency if you call into CPython (explicitly). Indeed creating such standalone executables simplifies the deployment and packaging issues: all the packages must be resolved at compile time, once you compile your application, there are no more dependencies on your Python packages (unless any of them calls into CPython of course).
> One thing which I didn't understand from the homepage: can I take vanilla Python code and AOT compile it with this?
Only if that vanilla Python compiles with LPython (since any LPython code is just Python code, a subset). So in general no. If you call CPython from your LPython main program (let's say), then you will get a small binary that depends on CPython to call into your Python code. I thought about somehow packaging the Python sources into the executable, similar to how PyOxidizer does it, but that's a project on its own almost. We will see what the community wants. If we can make LPython support a large enough subset of CPython, I think I would like to use LPython as is, since it's nice to not have any Python dependency and everything being high performance, essentially equivalent to writing C++ or Fortran.
Looks interesting! Thank you for focusing on AoT compilation and not just JIT compilation. To be honest, I'm sick of JIT compilation. In theory it seems like the best of both worlds, but in practice it turns out to be the worst of both worlds, especially for larger projects.
Will LPython have the ability to generate AoT compiled libraries in addition to executables?
Will LPython have the ability to generate AoT compiled libraries in addition to executables?
> Looks interesting! Thank you for focusing on AoT compilation and not just JIT compilation. To be honest, I'm sick of JIT compilation. In theory it seems like the best of both worlds, but in practice it turns out to be the worst of both worlds, especially for larger projects.
Indeed, I think for large projects you want:
* generate a binary
* fast compilation in Debug mode
* fast runtime in Release mode
Sometimes you want JIT, so we support it too, but I personally don't use it, I write the main program in LPython and just compile it to a binary.
> Will LPython have the ability to generate AoT compiled libraries in addition to executables?
Yes, you can do it today. Just compile to `.o` file and create a library. We use this library feature in production at my company today. If you run into issues, just ask us, we'll help.
Indeed, I think for large projects you want:
* generate a binary
* fast compilation in Debug mode
* fast runtime in Release mode
Sometimes you want JIT, so we support it too, but I personally don't use it, I write the main program in LPython and just compile it to a binary.
> Will LPython have the ability to generate AoT compiled libraries in addition to executables?
Yes, you can do it today. Just compile to `.o` file and create a library. We use this library feature in production at my company today. If you run into issues, just ask us, we'll help.
Fantastic, looking forward to trying this out!
And good point about JIT--it does have its place. What I should have said is that I wish there were better options with high quality support for _both_ AoT and JIT. Most of the options I'm aware of have good support for one, but poor or no support for the other. I'm curious to see how well LPython bridges the gap.
And good point about JIT--it does have its place. What I should have said is that I wish there were better options with high quality support for _both_ AoT and JIT. Most of the options I'm aware of have good support for one, but poor or no support for the other. I'm curious to see how well LPython bridges the gap.
Definitely let us know any feedback once you try it. You can open up an issue at lpython github.
I wish there were comparisons with Cython 3.0, which seems like it would be a competitor with the AOT part of what they are doing. For some reason they don’t mention Cython at all.
Hi William, nice to hear from you. We mention Cython at our front page (at the bottom): https://lpython.org/, together with the other 23 Python compilers that I know about (all of them are competitors, in a way). I am very familiar with Cython from about 10 years ago, but I have not followed the very latest developments. We can do a compilation time and runtime speed benchmarks against Cython in the next blog post. :)
It would also be nice to add some comparison with pythran, which seems to occupy a similar niche (although it can actually compile numpy code to optimized c++ code which I don't think python can do?)
Yes, we can compare with pythran too. We should really compare against all the other compilers, but it's a lot of work to compare meaningfully: we don't want to put up benchmarks unless we are really sure they are solid, and as everyone knows, it's really hard to do benchmarks that are fair, as one has to have solid experience with both projects being benchmarked. But we did Numba and C++, so you for now you can compare pythran against them to get a decent idea.
A new Python high-performance compiler that could compete with Mojo before it even releases.
Mojo is vaporware for now, they still don't support classes. There are many other issues, but good luck finding a meaningful size python codebase with zero classes.
Who are all these people that so strongly believe in mojo before even having written a single line of it (yes I'm aware you can write "mojo" in their walled-garden). Like they've gotta be paid shills because I can't fathom any other way one could be so confident that it'll trounce everything when it doesn't even exist yet.
Neither does LPython yet, even when it does it seems like LPython is meant as a Numba alternative, not something to run arbitrary Python code.
"LPython is built from the ground up to translate numerical, array-oriented code into simple, readable, and fast code."
"LPython is built from the ground up to translate numerical, array-oriented code into simple, readable, and fast code."
Yes, LPython is a strict subset of Python, while Mojo is a strict superset of Python.
Both are valid and consistent approaches with their pros and cons, I listed some of them here: https://fortran-lang.discourse.group/t/fast-ai-mojo-may-be-t....
Both are valid and consistent approaches with their pros and cons, I listed some of them here: https://fortran-lang.discourse.group/t/fast-ai-mojo-may-be-t....
> while Mojo is a strict superset of Python
Is it superset if it doesn't implement all of Python? It seems more like a set that has a non-empty intersection with Python.
Is it superset if it doesn't implement all of Python? It seems more like a set that has a non-empty intersection with Python.
My understanding from Mojo's plans is that they want to compile all of Python via their compiler (eventually), and then extend Python with extra syntax that will compile to high performance. I think right now they might not compile all of Python yet, so you are right they are neither a subset nor a superset, but once they deliver on their plans, they will become a superset.
A particular advantage of subsetting the language is that LPython inherits all the tooling of Python. I use pudb and PyCharm daily to develop LPython code.
Looks very interesting !
The authors talk about Numba, but does anyone know how it would compare to Codon ? (https://news.ycombinator.com/item?id=33908576)
edit: after trying quickly, it seems that lpython really requires type annotations everywhere, while codon is more permissive (or does type inference)
edit: after trying quickly, it seems that lpython really requires type annotations everywhere, while codon is more permissive (or does type inference)
I would say LPython, Codon, Mojo and Taichi are structured similarly as compilers written in C++, see the links at the bottom of https://lpython.org/.
Internally they each parse the syntax to AST, then have some kind of an intermediate representation (IR), do some optimizations and generate code. The differences are in the details of the IR and how the compiler is internally structured.
Regarding the type inference, this is for a blog post on its own. See this issue for now: https://github.com/lcompilers/lpython/issues/2168, roughly speaking, there is implicit typing (inference), implicit declarations and implicit casting. Rust disallows implicit declarations and casting, but allows implicit typing. As shown in that issue they only meant to do single line implicit typing, but (by a mistake?) allowed multi-statements implicit typing (action at a distance). LPython currently does not allow any implicit typing (type inference). As documented at the issue, the main problem with implicit typing is that there is no good syntax in CPython that would allow explicit type declaration but implicit typing. Typically you get both implicit declaration and implicit typing, say in `x = 5`, this both declares `x` as a new variable as well as types it as integer. C++ and Rust does not allow implicit declarations (you have to use `auto` or `let` keywords) and I think we should not do either. We could do something like `x: var = 5`, but at that point you might as well just do `x: i32 = 5`, use the actual type instead of `var`.
Internally they each parse the syntax to AST, then have some kind of an intermediate representation (IR), do some optimizations and generate code. The differences are in the details of the IR and how the compiler is internally structured.
Regarding the type inference, this is for a blog post on its own. See this issue for now: https://github.com/lcompilers/lpython/issues/2168, roughly speaking, there is implicit typing (inference), implicit declarations and implicit casting. Rust disallows implicit declarations and casting, but allows implicit typing. As shown in that issue they only meant to do single line implicit typing, but (by a mistake?) allowed multi-statements implicit typing (action at a distance). LPython currently does not allow any implicit typing (type inference). As documented at the issue, the main problem with implicit typing is that there is no good syntax in CPython that would allow explicit type declaration but implicit typing. Typically you get both implicit declaration and implicit typing, say in `x = 5`, this both declares `x` as a new variable as well as types it as integer. C++ and Rust does not allow implicit declarations (you have to use `auto` or `let` keywords) and I think we should not do either. We could do something like `x: var = 5`, but at that point you might as well just do `x: i32 = 5`, use the actual type instead of `var`.
Shedskin is a Python-to-C++ transpiler that does type inference and does not support the full standard library: https://en.wikipedia.org/wiki/Shed_Skin#Type_inference
From "Show HN: Python Tests That Write Themselves" (2019) https://news.ycombinator.com/item?id=21012133:
> pytype (Google) [1], PyAnnotate (Dropbox) [2], and MonkeyType (Instagram) [3] all do dynamic / runtime PEP-484 type annotation type inference [4]
Hypothesis (@given decorator tests) also does type inference IIUC? https://hypothesis.readthedocs.io/en/latest/
icontract and pycontracts do runtime Preconditions and Postconditions with Design-by-Contract patterns similar to Eiffel DbC; they check the types and values of arguments passed while the program in running and not just at coding or compile time.
From "Show HN: Python Tests That Write Themselves" (2019) https://news.ycombinator.com/item?id=21012133:
> pytype (Google) [1], PyAnnotate (Dropbox) [2], and MonkeyType (Instagram) [3] all do dynamic / runtime PEP-484 type annotation type inference [4]
Hypothesis (@given decorator tests) also does type inference IIUC? https://hypothesis.readthedocs.io/en/latest/
icontract and pycontracts do runtime Preconditions and Postconditions with Design-by-Contract patterns similar to Eiffel DbC; they check the types and values of arguments passed while the program in running and not just at coding or compile time.
Yes, we have Shedskin in the list at the bottom of https://lpython.org/. Note that the Shedskin compiler is written in Python, so the speed of compilation might be lower than other Python compilers written in C++. Unless it compiles itself, that would be interesting. We thought about eventually writing LPython in LPython, but for now we are focusing on delivering, so we are sticking to C++.
This is awesome. Love to see competition as it tends to be very beneficial to end users.
I use Numba quite a bit to does up slow Pandas operations. Cool to have another alternative.
I use Numba quite a bit to does up slow Pandas operations. Cool to have another alternative.
Being able to JIT individual Python functions is absolutely huge, this could make way for huge speedups in hot functions from existing large Python codebases.
that's what Numba does.
Numba seems specialized for NumPy. LPython seems to work with everything, almost similar to mypyc.
It's not that specific to Numpy, it deals with all kinds of properly typed Python as long as no packages are used. In fact you don't need Numba if you're already using proper Numpy code.
Yes, the Numba use case is a subset of LPython. We want to support what Numba does, that is, you decorate your function and JIT it. But in addition, we also want to compile to binaries (ahead of time) that have no CPython dependency, and support high performance optimizations. Numba speeds up Python a lot, but doesn't seem to quite get the Fortran/C++ level of performance sometimes. One of our main goals is to be able to get maximum performance, so that eventually as a user you can depend on LPython that if it compiles it, it will run at least as fast as C++ or Fortran would.
> At least as fast as C++ or Fortran
That obviously has to be the goal, but is it really feasible to be faster than good C/C++ or Fortran? I did some research into the Python Compiler landscape and came to the conclusion that it almost always boils to LLVM. So, if you want to have fast code, just help the compiler make the most of your code and you'll be 99% of the way there and as fast as possible without significantly more effort.
Would you agree with my layman's understanding of this topic?
That obviously has to be the goal, but is it really feasible to be faster than good C/C++ or Fortran? I did some research into the Python Compiler landscape and came to the conclusion that it almost always boils to LLVM. So, if you want to have fast code, just help the compiler make the most of your code and you'll be 99% of the way there and as fast as possible without significantly more effort.
Would you agree with my layman's understanding of this topic?
It's harder to imagine for a Python compiler, so let's just focus on LFortran (since LPython delivers exactly the same performance, due to sharing the middle end and backends). The Fortran compilers traditionally were faster than C++, and almost always (even today) are at least as fast as C++, due to the Fortran language being simpler and higher level, designed to allow good optimizations. LFortran competes with other compilers as well as C++ compilers and our goal indeed has to be to be at least as fast as the competition. We currently are sometimes faster sometimes slower, but we are in the same league, so that's a good start.
Regarding LLVM: my experience so far is that LLVM is indeed amazing what it can do in terms of optimizations. It's very very good. However, it is not all LLVM. As our benchmarks in the blog post show, we compare Numba, Clang and LPython, all three of which use LLVM. But we get vastly different performance for what seems to look like identical initial code. To know exactly why, we would have to meet with the Numba and Clang developers and study this, I suspect Clang lowers to LLVM too soon, and uses C++ to do abstractions (like `std::vector` or `std::unordered_map`) and perhaps it can't quite get the top performance this way. Numba perhaps doesn't get all the types as tight as LPython, or perhaps implements some things not as efficiently, or perhaps doesn't apply as good optimizations before lowering to LLVM. I suspect LLVM gets the best performance if the compiler generates as straightforward LLVM IR code as possible, without layers and layers of abstractions that might not end up being "zero cost" in practice.
Regarding LLVM: my experience so far is that LLVM is indeed amazing what it can do in terms of optimizations. It's very very good. However, it is not all LLVM. As our benchmarks in the blog post show, we compare Numba, Clang and LPython, all three of which use LLVM. But we get vastly different performance for what seems to look like identical initial code. To know exactly why, we would have to meet with the Numba and Clang developers and study this, I suspect Clang lowers to LLVM too soon, and uses C++ to do abstractions (like `std::vector` or `std::unordered_map`) and perhaps it can't quite get the top performance this way. Numba perhaps doesn't get all the types as tight as LPython, or perhaps implements some things not as efficiently, or perhaps doesn't apply as good optimizations before lowering to LLVM. I suspect LLVM gets the best performance if the compiler generates as straightforward LLVM IR code as possible, without layers and layers of abstractions that might not end up being "zero cost" in practice.
Thanks for the reply. I appreciate it.
There are things you cannot do with numpy and that numba helps with, eg a custom PDE solver where you cannot avoid iterating over arrays' elements.
Some things can’t be vectorized and sometimes the vectorized implementation requires too much intermediate memory.
This is really exciting!
Does typing have to be extensive or does the majority of it get inferred with perhaps just function and class boundaries needing annotations?
And if the latter, does the typing get inferred _after_ the initial ssa pass, so a name has a context-specific type?
Does typing have to be extensive or does the majority of it get inferred with perhaps just function and class boundaries needing annotations?
And if the latter, does the typing get inferred _after_ the initial ssa pass, so a name has a context-specific type?
See my comment here for all the details regarding implicit typing and why we don't currently do it: https://news.ycombinator.com/item?id=36920963. But we give you nice error messages if types don't match.
This is way too similar to Mojo (language) by Modular. At least at some level conceptually. All in a good way.
I think - the performance gains are coming from the Python syntax being transliterated to an LFortran intermediate representation (much like Numba converts code to LLVM IR).
Any calls to CPython libraries are made using a special decorator, which might be doing interop using the CPython API. My guess is, this will come with a performance penalty. More so if you’re using Numpy or Scipy, as you’ll be going through several layers of abstractions and hand-offs.
This is because Numba, Pythran and JAX (in a way) get around this by reimplementing a subset of Numba/Scipy/other core libraries. Any call to a supported function is dynamically rerouted to the native reimplementation during JIT/AOT compilation.
I’d be interested in seeing how far LPython can tolerate regular Python code, with a ton of CPython interop and class use.
In any case, glad to see more competition. Not to take anything from the authors - this is a massive effort on their part and achieves some impressive results. Mojo has VP money behind it - AFAIK, this is a pure volunteer driven effort, and I’m grateful to the authors for doing it!
I think - the performance gains are coming from the Python syntax being transliterated to an LFortran intermediate representation (much like Numba converts code to LLVM IR).
Any calls to CPython libraries are made using a special decorator, which might be doing interop using the CPython API. My guess is, this will come with a performance penalty. More so if you’re using Numpy or Scipy, as you’ll be going through several layers of abstractions and hand-offs.
This is because Numba, Pythran and JAX (in a way) get around this by reimplementing a subset of Numba/Scipy/other core libraries. Any call to a supported function is dynamically rerouted to the native reimplementation during JIT/AOT compilation.
I’d be interested in seeing how far LPython can tolerate regular Python code, with a ton of CPython interop and class use.
In any case, glad to see more competition. Not to take anything from the authors - this is a massive effort on their part and achieves some impressive results. Mojo has VP money behind it - AFAIK, this is a pure volunteer driven effort, and I’m grateful to the authors for doing it!
Well, a couple key differences from Mojo are 1) LPython is open source (BSD 3-clause), and 2) LPython is available to download and use locally today. Mojo is still only available on private Modular notebooks.
Granted, I'm optimistic for Mojo's potential but I do wish I could run it locally. Modular's pricing model also remains to be seen.
Granted, I'm optimistic for Mojo's potential but I do wish I could run it locally. Modular's pricing model also remains to be seen.
Thank you for the encouragement. I can answer / clarify your comments:
> This is way too similar to Mojo (language) by Modular. At least at some level conceptually. All in a good way.
Yes, the main difference is that Mojo is (or will be) a strict superset of Python, while we are a strict subset (but you can call the rest of Python via a decorator).
> I think - the performance gains are coming from the Python syntax being transliterated to an LFortran intermediate representation (much like Numba converts code to LLVM IR).
Correct. We use the same IR as LFortran and then we lower to LLVM IR.
> Any calls to CPython libraries are made using a special decorator, which might be doing interop using the CPython API. My guess is, this will come with a performance penalty. More so if you’re using Numpy or Scipy, as you’ll be going through several layers of abstractions and hand-offs.
Yes, it calls CPython, so it's slow.
> This is because Numba, Pythran and JAX (in a way) get around this by reimplementing a subset of Numba/Scipy/other core libraries. Any call to a supported function is dynamically rerouted to the native reimplementation during JIT/AOT compilation.
We do as well: we support a subset of NumPy directly (eventually most of NumPy). We also support a very small subset of SymPy. Over time we add more support to more basic libraries. The rest you can call via CPython, but slow. For SymPy we'll experiment building it on top (at least some modules, like limits) and compile using LPython. Given that any LPython code is just Python, this might be a viable way, as long as we support enough of Python directly.
> I’d be interested in seeing how far LPython can tolerate regular Python code, with a ton of CPython interop and class use.
We support structs via `@dataclass`, but not classes yet (although LFortran does to some extent, so we'll add support soon to LPython as well). For regular Python call LPython will give nice error messages suggesting to type things. Once you do and it compiles, it will run fast.
> In any case, glad to see more competition. Not to take anything from the authors - this is a massive effort on their part and achieves some impressive results. Mojo has VP money behind it - AFAIK, this is a pure volunteer driven effort, and I’m grateful to the authors for doing it!
We are supported by my current company (GSI Technology) as well as by NumFOCUS (LFortran), GSoC and other places; we have a very strong team (5 to 10 people). In the past I was supported by Los Alamos National Laboratory to develop LFortran. I have delivered SymPy as a physics student with no institutional support. So I have experience doing a lot with very little. :)
> This is way too similar to Mojo (language) by Modular. At least at some level conceptually. All in a good way.
Yes, the main difference is that Mojo is (or will be) a strict superset of Python, while we are a strict subset (but you can call the rest of Python via a decorator).
> I think - the performance gains are coming from the Python syntax being transliterated to an LFortran intermediate representation (much like Numba converts code to LLVM IR).
Correct. We use the same IR as LFortran and then we lower to LLVM IR.
> Any calls to CPython libraries are made using a special decorator, which might be doing interop using the CPython API. My guess is, this will come with a performance penalty. More so if you’re using Numpy or Scipy, as you’ll be going through several layers of abstractions and hand-offs.
Yes, it calls CPython, so it's slow.
> This is because Numba, Pythran and JAX (in a way) get around this by reimplementing a subset of Numba/Scipy/other core libraries. Any call to a supported function is dynamically rerouted to the native reimplementation during JIT/AOT compilation.
We do as well: we support a subset of NumPy directly (eventually most of NumPy). We also support a very small subset of SymPy. Over time we add more support to more basic libraries. The rest you can call via CPython, but slow. For SymPy we'll experiment building it on top (at least some modules, like limits) and compile using LPython. Given that any LPython code is just Python, this might be a viable way, as long as we support enough of Python directly.
> I’d be interested in seeing how far LPython can tolerate regular Python code, with a ton of CPython interop and class use.
We support structs via `@dataclass`, but not classes yet (although LFortran does to some extent, so we'll add support soon to LPython as well). For regular Python call LPython will give nice error messages suggesting to type things. Once you do and it compiles, it will run fast.
> In any case, glad to see more competition. Not to take anything from the authors - this is a massive effort on their part and achieves some impressive results. Mojo has VP money behind it - AFAIK, this is a pure volunteer driven effort, and I’m grateful to the authors for doing it!
We are supported by my current company (GSI Technology) as well as by NumFOCUS (LFortran), GSoC and other places; we have a very strong team (5 to 10 people). In the past I was supported by Los Alamos National Laboratory to develop LFortran. I have delivered SymPy as a physics student with no institutional support. So I have experience doing a lot with very little. :)
Thanks for creating SymPy! LPython is genuinely impressive. I am excited to give it a try, and I hope to see it flourish!
Thank you! Please report all bugs that you find once you try it.
Is the name chosen in contrast with PyPy's RPython?
Haven't heard from pypy for a while now.
Haven't heard from pypy for a while now.
No, we had LFortran, so naturally we have LPython now as the second frontend. We chose "L" in LFortran to be unspecified, although let's just say I live in Los Alamos, and we use LLLVM.
PyPy is still around. We released a Python3.10 version last month. What else would you like to hear about?
I'm not the person who asked, but I've always been curious what the "long pole in the tent" is for pypy updates. https://mail.python.org/archives/list/[email protected]/ seems pretty quiet, the blog seems to be just announcements and not technical dives, and the 3.11 milestone ( https://foss.heptapod.net/pypy/pypy/-/milestones/15#tab-issu... ) just has one issue
Please don't take this as "why u no faster?!" as much as I really would enjoy understanding what it takes to bring pypy up to cpython parity. I do see https://doc.pypy.org/en/latest/contributing.html#your-first-... says that pypy has a lot of layers and (I'd suppose) a fraction of the number of people compared to cpython's contributor base, but like I said it's hard to understand from the outside whether it's just a lot of rocks to break, or there are genuine novel optimization or computer science tricks that have to be solved when rolling out a newer version
Above all, thanks so much for your work on pypy - it has really helped me a lot and not from its speed but from my ability to use in in places where getting cpython to run is harder than "curl pypy.tar.bz2 | tar -xjf"
Please don't take this as "why u no faster?!" as much as I really would enjoy understanding what it takes to bring pypy up to cpython parity. I do see https://doc.pypy.org/en/latest/contributing.html#your-first-... says that pypy has a lot of layers and (I'd suppose) a fraction of the number of people compared to cpython's contributor base, but like I said it's hard to understand from the outside whether it's just a lot of rocks to break, or there are genuine novel optimization or computer science tricks that have to be solved when rolling out a newer version
Above all, thanks so much for your work on pypy - it has really helped me a lot and not from its speed but from my ability to use in in places where getting cpython to run is harder than "curl pypy.tar.bz2 | tar -xjf"
I am glad you find PyPy useful. The good news is exactly the boring consistency with which we have been able, on a volunteer basis, to stay pretty close to CPython progress. There are no big challenges there, it is work at the top layer of the interpreter to adapt current code to CPython changes. On the other hand, we need sponsorship to implement the deeper changes we would like to make that would make things even faster.
Looks really cool. Build on windows fails for me, are there any downloadable prebuilt binaries to try lpython quickly ?
Yes, try `conda install -c conda-forge lpython`. It should work on Windows, but it's not as extensively tested as macOS and Linux. If it doesn't work, please report it, and we'll fix it. Once we get to beta, we will support Windows very well.
It worked, thanks !
> Based on the novel Abstract Semantic Representation (ASR) shared with LFortran,
What's novel about it?
What's novel about it?
ASR abstracts away all syntax and all details of the target machine, no leaks. Contrast to the schoolbook approach of decorating ASTs with semantic information, which often reflects details of a target machine.
Implication is that ASR is a full programming language in its own right (though with no quality-of-life features: everything is explicit, and it's also currently restricted to the operations featured by LFortran and LPython: heavily array-oriented for now, ASR grows as LFortran and LPython grow). I've prototyped, in Clojure, an independent type-checker for ASR (https://github.com/rebcabin/masr), and an interpreter (for "abstract execution") should not be difficult.
Sometimes, standard semantical approaches assume a target stack-machine, or SSA architecture, or something else with insufficient generality to cover all the cases we want (e.g., non-Von architectures like APU from GSIT). ASR assumes only lambda/pi/rho calculus, depending on whether you want concurrency semantics (that's TBD, frankly; today it's justs lambda)
Yes. ASR is as abstract as it can be, but it is still faithful to the original language, no information has been lost, nothing was lowered.
Right. Decompilation with ASR should be relatively easy and more faithful than average decompilation (though, as mentioned by another commenter, the very-long-term value of decompilation in general is debatable in the face of rising AI like CoPilot).
How do you manage to do that for Python AND Fortran in the same language?
By being a superset of Fortran and subset of Python. It turns out the features map on each other almost 1:1, and the differences can be taken care of by the respective frontends, so the abstracted ASR maps perfectly.
This is dope, I think the benchmarks of speed for python marks it way slower than C++, JS.
If this could be used in mainstream web dev with the level of speed detailed, python might eat Javascript's lunch.
*bias - python obsessed
If this could be used in mainstream web dev with the level of speed detailed, python might eat Javascript's lunch.
*bias - python obsessed
Speed isn't usually high on the list for web development, I create APIs for fintech and we use nestJS for the back end, and nest is definitely slower but you get a lot of benefits that make it completely worth it.
Auto swagger generation, validation pipes and so on.
Auto swagger generation, validation pipes and so on.
completely fair, fintech is a beast that requires a lot of blood sweat and tears
> You can install it using Conda
On the risk of starting a holywar: why.
On the risk of starting a holywar: why.
It was the easiest for us to deliver a binary that works on Linux, macOS and Windows. Others can then use this binary as a reference to package LPython into other distributions. You can also install LPython from source, but it's harder than just using the binary that we built correctly (with all optimizations on, etc.).
Miniconda can be nice sharing an environment around especially with Apple Silicon as one of targets.
truely amazing work. As it is a subset of python, where can I find what is supported and what is not supported?
I think today with things like CoPilot that speeds up development significantly the era of python and untyped languages is past its peak.
Yes, I thought about this too. Also LLMs can or will be able to translate from one language to another, so perhaps the fact that LFortran/LPython can translate Fortran/Python to other languages like C++ or Julia might not be useful.
My approach is that it is still unclear to me what exactly will be possible in the future, while I know exactly how to deliver these compilers today. I suspect a traditional compiler will be more robust and also a lot faster than an LLM for tasks like translation to another language or compilation to binary. And speed of compilation is very important for development from the user perspective.
Conclusion: I don't know what the future will bring, but I suspect these compilers will still be very useful.
My approach is that it is still unclear to me what exactly will be possible in the future, while I know exactly how to deliver these compilers today. I suspect a traditional compiler will be more robust and also a lot faster than an LLM for tasks like translation to another language or compilation to binary. And speed of compilation is very important for development from the user perspective.
Conclusion: I don't know what the future will bring, but I suspect these compilers will still be very useful.
Some IDEs have incremental compilers that are sufficiently fast to update squigglies and what-not on every keystroke. Compilation speed is a primary value, in general.
Always wonder how well are these compilers doing if I am already writing full on SIMD codes instead of crappy for loops?
You're writing SIMD with Python? That's impressive. How are you doing that?
Depends. Does Numba help you?
What does this do with garbage collection? How does it choose between stack and heap allocations?
It doesn't do garbage collection. Variables and arrays get deallocated when they go out of scope (similar to C++ RAII). When you return from a function, it will be a copy, although I think we elide the copy in most cases. We restrict the Python subset in such a way that this exactly works with both LPython and CPython.
Local variables are on stack. Lists, dicts, sets and arrays use heap, unless the length is known at compile time, where we might use a stack, but I think we need to make it configurable, since one can run out of stack quite easily this way.
Local variables are on stack. Lists, dicts, sets and arrays use heap, unless the length is known at compile time, where we might use a stack, but I think we need to make it configurable, since one can run out of stack quite easily this way.
At least as fast as C++ is a bold claim, but this is an interestingly documented process. I'm keen.
I'm quite partial to Nuitka at this point, but I'm open to other Python compilers.