Language Summit 2022: WebAssembly: Python in the browser and beyond

https://us.pycon.org/2022/events/language-summit/

WebAssembly: Python in the browser and beyond, Christian Heimes

Brett, Ethan Smith, and I have been working on WebAssembly support for Python 3.11. CPython main branch now compiles to WASM, runs in modern browsers, and even the test suite passes under NodeJS with any additional modifications or patches. But WASM is not just for the web. WASI and lightweight runtimes like wasmtime can run WASM code on server-side at near native code performance in a sandbox.

In my presentation I will give you a short introduction to WASM, how it can be used to run CPython in browsers, in sandboxing for edge computing, and how wasmtime-py might solve some pain points with distribution of native code extensions. Better browser and WASI integration is going to require more changes to the interpreter core and stdlib. What kind of changes would be acceptable?

Transcript

1. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
   Language Summit @ PyCon US 2022
   WebAssembly:
   Python in the browser & beyond
   Christian Heimes
   Principal Software Engineer
   christian@python.org cheimes@redhat.com
   1
   @ChristianHeimes
   

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2. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
   caniuse.com/wasm ?
   2
   Modern browsers support
   two programming languages
   Wasmer
   wasmtime
   Node
   

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3. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
   3
   Compiling to WASM
   human code to native machine code
   C
   C++
   Go
   Rust
   frontend
   frontend
   frontend
   frontend
   intermediate
   representation
   backend
   backend
   backend
   backend
   x86_64
   i686
   aarch64
   armv7
   backend wasm32
   Emscripten SDK
   

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4. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
   4
   def line(a, x, b):
   return a * x + b
   double
   line(double a, double x, double b) {
   return a * x + b;
   }
   What is WebAssembly?
   C/C++
   

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5. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
   5
   # WASM text (WAT)
   (module
   (export "line" (func $line))
   (func $line (param $a f64)
   (param $x f64)
   (param $b f64)
   (result f64)
   get_local $a
   get_local $x
   f64.mul
   get_local $b
   f64.add
   )
   )
   Stack machine VM
   >>> import dis
   >>> def line(a, x, b):
   ... return a * x + b
   ...
   >>> dis.dis(line)
   2 0 LOAD_FAST 0 (a)
   2 LOAD_FAST 1 (x)
   4 BINARY_MULTIPLY
   6 LOAD_FAST 2 (b)
   8 BINARY_ADD
   10 RETURN_VALUE
   

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6. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
   Opening a file on disk
   6
   open("file.txt")
   _io.TextIOWrapper
   _io.BufferedReader
   _io.FileIO
   // _io/fileio.c
   #include
   int fd = open(
   path, flags, ...
   );
   glibc
   libc.so.6
   open(path, ...);
   openat(
   dirfd, path, ...
   );
   syscall(
   SYS_openat,
   dirfd,
   path, ...
   );
   open
   Kernel
   sys_call_table
   ...
   VFS
   ext4fs
   block device
   SATA
   ...
   syscall
   

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7. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
   7
   Problems
   ▸ Linux, macOS, Windows, … have different APIs
   ▸ Linux syscall numbers are arch-specific
   x86_64: 257, i686: 295, ARM: 332, aarch64: 56, ...
   ▸ Browsers are sandboxed
   How to open a file safely on all platforms?
   (import "env" "__syscall_openat"
   (func $fimport$1 (param i32 i32 i32 i32) (result i32)))
   (import "wasi_snapshot_preview1" "fd_read"
   (func $fimport$2 (param i32 i32 i32 i32) (result i32)))
   (import "wasi_snapshot_preview1" "fd_close"
   (func $fimport$0 (param i32) (result i32)))
   

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8. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
   Opening a file on Emscripten / WASI
   8
   open("file.txt")
   _io.TextIOWrapper
   _io.BufferedReader
   _io.FileIO
   // _io/fileio.c
   #include
   int fd = open(
   path, flags, ...
   );
   musl static
   libc.a
   open(path, ...);
   openat(
   dirfd, path, ...
   );
   syscall(
   SYS_openat,
   dirfd,
   path, ...
   );
   open
   Browser
   NodeJS
   WASM
   import / export
   WASI
   runtime
   MEMFS
   NODE raw FS
   

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9. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
   9
   ▸ x86_64-unknown-linux-gnu
   ▸ x86_64-unknown-linux-musl
   ▸ armv7l-unknown-linux-gnueabihf
   ▸ aarch64-unknown-linux-android
   ▸ aarch64-apple-darwin
   ▸ i686-pc-windows-msvc
   ▸ sparcv9-sun-solaris
   ▸ wasm32-emscripten
   ▸ wasm32-wasi
   Target Triple(t)
   machine vendor os (abi)
   "CPU" "OS"
   

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10. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    10
    What is WebAssembly
    ▸ "machine-independent machine code"
    ▸ binary (.wasm), text (.wat) with metadata
    ▸ designed to be portable and fast
    ▸ 4 value types (integer i32, i64; float f32, f64)
    ▸ ~200 instructions
    ▸ optional extension (128 bits vector ops, threading)
    ▸ wasm modules have
    ･ imports
    ･ exports
    ･ memory
    

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11. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    Cross-compile with Emscripten
    11
    EMSDK
    ▸ build system: x86_64-pc-linux-gnu
    ▸ target host: wasm32-unknown-emscripten
    ▸ cross compiler: emcc
    (Python script, Clang, LLVM, Binaryen, NodeJS)
    ▸ sysroot (headers, libraries)
    ▸ configure wrapper: emconfigure
    ▸ make wrapper: emmake
    

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12. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    Cross compiling improvements
    12
    ▸ new wasm32 targets
    ▸ new --with-build-python
    ▸ re-implement _freeze_module in
    pure Python
    ▸ detect module deps in configure
    ▸ Modules/Setup.stdlib
    ▸ improved config.cache
    ▸ VPATH / out-of-tree build fixes
    ▸ new --with-emscripten-target
    # Makefile
    MODULE_ZLIB=yes
    MODULE_ZLIB_CFLAGS=
    MODULE_ZLIB_LDFLAGS=-lz
    MODULE__SCPROXY=n/a
    # Setup.stdlib.in
    @MODULE__SCPROXY_TRUE@_scproxy _scproxy.c
    @MODULE_ZLIB_TRUE@zlib zlibmodule.c
    # Setup.stdlib
    #_scproxy _scproxy.c
    zlib zlibmodule.c
    

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13. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    13
    Build Python for browsers
    $ git clone
    https://github.com/python/cpython.git
    $ cd cpython
    $ mkdir -p builddir/build
    $ mkdir -p builddir/emscripten-browser
    $ cd builddir/emscripten-browser
    $ CONFIG_SITE=config.site-wasm32-emscripten \
    emconfigure ../../configure \
    --host=wasm32-unknown-emscripten \
    --build=x86_64-pc-linux-gnu \
    --with-emscripten-target=browser \
    --with-build-python=$(pwd)/../build/python
    $ emmake make
    $ cd builddir/build
    $ ../../configure
    $ make
    $ ls python
    python
    $ cd ../..
    $ ls python*
    python.data python.html python.js python.wasm
    python.worker.js
    # config site
    ac_cv_func_eventfd=no
    ac_cv_func_memfd_create=no
    

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14. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    14
    How it's going
    2022-04-05 / 2022-03-21
    $ node --experimental-wasm-threads \
    --experimental-wasm-bulk-memory \
    python.js -m test -w
    == CPython 3.11.0a7+
    (heads/bpo-40280-smaller-build-dirty:eb79f02293d, Apr 8
    2022, 10:58:59) [Clang 15.0.0
    (https://github.com/llvm/llvm-project
    80ec0ebfdc5692a58e0832125f2c
    == Emscripten-1.0-wasm32-32bit little-endian
    == cwd:
    /python-wasm/cpython/builddir/emscripten-node/build/test_pyt
    hon_42æ
    == CPU count: 8
    == encodings: locale=UTF-8, FS=utf-8
    0:00:00 load avg: 0.10 Run tests sequentially
    0:00:00 load avg: 0.10 [ 1/435] test_grammar
    0:00:00 load avg: 0.10 [ 2/435] test_opcodes
    ...
    == Tests result: SUCCESS ==
    342 tests OK.
    92 tests skipped.
    Total duration: 12 min 22 sec
    Tests result: SUCCESS
    
    

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15. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    15
    Platform
    >>> sys.platform
    'emscripten'
    >>> os.name
    'posix'
    >>> sys._emscripten_info
    sys._emscripten_info(
    emscripten_version=(3, 1, 8),
    runtime='Mozilla/5.0 (X11; Fedora; Linux x86_64;
    rv:99.0) Gecko/20100101 Firefox/99.0',
    pthreads=False,
    shared_memory=False)
    >>> os.uname()
    posix.uname_result(sysname='Emscripten',
    nodename='emscripten', release='1.0',
    version='#1', machine='wasm32')
    EM_JS(char *, _Py_emscripten_runtime, (void), {
    var info;
    if (typeof navigator == 'object') {
    info = navigator.userAgent;
    } else if (typeof process == 'object') {
    info = "Node.js ".concat(process.version)
    } else {
    info = "UNKNOWN"
    }
    var len = lengthBytesUTF8(info) + 1;
    var res = _malloc(len);
    stringToUTF8(info, res, len);
    return res;
    });
    

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16. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    > 60 CPython pull requests
    16
    https://bugs.python.org/issue40280
    $ ./run-python-node.sh -c 'import _zoneinfo'
    builddir/emscripten-node/python.js:147
    throw ex;
    ^
    Error [RuntimeError]: function signature mismatch
    at module_dealloc (wasm-function[1908])
    at _Py_Dealloc (wasm-function[1986])
    at insertdict (wasm-function[1652])
    at _PyDict_SetItem_Take2 (wasm-function[1641])
    at dict_ass_sub (wasm-function[1733])
    at PyObject_SetItem (wasm-function[495])
    at finalize_modules (wasm-function[3677])
    at Py_FinalizeEx (wasm-function[3674])
    at Py_RunMain (wasm-function[4057])
    at pymain_main (wasm-function[4060])
    Emitted 'error' event on process instance at:
    at emitUnhandledRejectionOrErr
    at MessagePort.[nodejs.internal.kHybridDispatch]
    at MessagePort.exports.emitMessage
    --- a/Modules/_zoneinfo.c
    +++ b/Modules/_zoneinfo.c
    @@ -2612,7 +2612,7 @@ static PyTypeObject
    PyZoneInfo_ZoneInfoType = {
    // Specify the _zoneinfo module
    static PyMethodDef module_methods[] =
    {{NULL, NULL}};
    static void
    -module_free(void)
    +module_free(void *m)
    {
    

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17. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    Emscripten bug fixes
    17
    https://github.com/ethanhs/python-wasm/issues/43
    ▸ Segfault in freeaddrinfo, memory leak in getaddrinfo
    ▸ clock_nanosleep() sleeps forever
    ▸ strftime() mishandles quoted percent, e.g. %%z
    ▸ week number of strftime("%U") and %W
    ▸ Fix edge case in strftime %V (ISO 8601 week number)
    ▸ opendir() leak file descriptor on error
    ▸ msync() on anon mapping fails with JS TypeError
    ▸ utimensat() sets wrong atime and mtime
    ▸ Blocking socket accept() fails with JS TypeError
    

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18. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    JupyterLite
    18
    SDK
    CPython
    REPL
    ⁉
    Browser Server
    

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19. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    19
    Browser
    ❌ subprocess (fork, exec)
    ❌ threads
    ❌ file system (only MEMFS)
    🚧 shared extension modules
    ❌ PyPI packages
    ❓ sockets
    ❌ urllib, asyncio
    ❌ signals
    Node
    ❌ subprocess (fork, exec)
    ✅ threads
    ✅ file system (Node raw FS)
    🚧 shared extension modules
    ❌ PyPI packages
    ❓ sockets
    ❌ urllib, asyncio
    🚧 signals
    Supported features
    CPython 3.11 alpha 7
    Pyodide
    ❌ subprocess (fork, exec)
    🚧 threads
    ✅ file system (IDB, Node, …)
    ✅ shared extension modules
    ✅ PyPI packages
    ✅ WebAPI fetch / WebSocket
    ✅ signals
    

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20. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    What has WASM ever done for us?
    20
    ▸ Run Python anywhere (including Android, iOS)
    ･ great for education (no installation required)
    ･ easy sharing of programs (platform-independent code)
    ･ secure (browser are sandboxes)
    ▸ App development
    ▸ WASI (WASM on the server) for edge computing
    ･ small runtime with JIT / AOT optimization
    ･ capability-based sandbox
    ▸ platform- and OS-agnostic binary wheels?
    

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21. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    21
    Executable docs and examples
    Trey Hunner: www.pythonmorsels.com/paste/
    

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22. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    Paul m. p. P. https://pmp-p.github.io/pygame-wasm/
    22
    

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23. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    JupyterLite
    Jupyter ❤ WebAssembly ❤ Python
    jupyterlite.github.io/demo/lab/
    23
    

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24. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    24
    ▸ numpy-1.22.3-cp310-cp310-win_amd64.whl
    ▸ numpy-1.22.3-cp310-cp310-win32.whl
    ▸ numpy-1.22.3-cp310-cp310-manylinux_2_17_x86_64.manylinux2014_x86_64.whl
    ▸ numpy-1.22.3-cp310-cp310-manylinux_2_17_aarch64.manylinux2014_aarch64.whl
    ▸ numpy-1.22.3-cp310-cp310-macosx_11_0_arm64.whl
    ▸ numpy-1.22.3-cp310-cp310-macosx_10_14_x86_64.whl
    ▸ numpy-1.22.3-cp39-cp39-win_amd64.whl
    ▸ numpy-1.22.3-cp39-cp39-win32.whl
    ▸ numpy-1.22.3-cp39-cp39-manylinux_2_17_x86_64.manylinux2014_x86_64.whl
    ▸ numpy-1.22.3-cp39-cp39-manylinux_2_17_aarch64.manylinux2014_aarch64.whl
    ▸ numpy-1.22.3-cp39-cp39-macosx_11_0_arm64.whl
    ▸ numpy-1.22.3-cp39-cp39-macosx_10_14_x86_64.whl
    ▸ numpy-1.22.3-cp38-cp38-win_amd64.whl
    ▸ numpy-1.22.3-cp38-cp38-win32.whl
    ▸ numpy-1.22.3-cp38-cp38-manylinux_2_17_x86_64.manylinux2014_x86_64.whl
    ▸ numpy-1.22.3-cp38-cp38-manylinux_2_17_aarch64.manylinux2014_aarch64.whl
    ▸ numpy-1.22.3-cp38-cp38-macosx_11_0_arm64.whl
    ▸ numpy-1.22.3-cp38-cp38-macosx_10_14_x86_64.whl
    numpy-1.22.3-cp311-abi3-wasm32.whl
    ▸ Python >= 3.11, <4
    ▸ Any OS
    ▸ Any CPU architecture
    Python binary extension hell
    3 Python versions, 3 CPU archs, 3 OSes: 18 wheels
    

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25. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    25
    wasmtime for Python
    github.com/bytecodealliance/wasmtime-py
    from functools import partial
    from wasmtime import Store, Module, Instance
    store = Store()
    module = Module(store.engine, """
    (module
    (export "line" (func $line))
    (func $line (param $a f64) (param $x f64)
    (param $b f64) (result f64)
    get_local $a
    get_local $x
    f64.mul
    get_local $b
    f64.add
    )
    )""")
    instance = Instance(store, module, [])
    line = instance.exports(store)["line"]
    line = partial(line, store)
    print(line(3., 5., 2.))
    # 17.0
    

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26. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    Discussion items
    26
    ▸ Tier 2 platform support (buildbot)
    ▸ Should we publicly pronounce official WASM support?
    ▸ Ship / provide official WASM binaries (CDN)?
    ▸ Use WASM to have runnable examples in documentation?
    ▸ Add browser API and Emscripten API modules?
    https://github.com/pmp-p/python-wasm-plus/tree/main/support/__EMSCRIPTEN__.embed
    ▸ Should we add a very high-level HTTPS API?
    sockets / networking in Emscripten is not compatible with urllib
    ▸ asyncio / async code?
    ▸ Reduce stdlib and binary size?
    ▸ Wizer support (WASM pre-initializer / memory freezer)
    

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27. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    Python on WebAssembly
    … a lot of opportunities!
    … a lot of work left to do!
    27
    ❤
    

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28. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    28
    ▸ https://bugs.python.org/issue40280
    ▸ https://github.com/ethanhs/python-wasm
    ▸ https://pyodide.org/
    ▸ https://pmp-p.github.io/pygame-wasm
    ▸ https://jupyterlite.github.io/demo/lab/
    ▸ https://assets.metacade.com/emulators/wi
    n311vr.html
    ▸ https://pypi.org/project/wasmtime/
    ▸ https://mbebenita.github.io/WasmExplorer/
    ▸ https://wasdk.github.io/WasmFiddle/
    ▸ David Beazley Keynote PyCon India 2019
    https://youtu.be/VUT386_GKI8
    ▸ Lin Clark: A Cartoon Intro to WebAssembly
    https://youtu.be/HktWin_LPf4
    Links & Resources
    https://repl.ethanhs.me
    https://cheimes.fedorapeople.org/python-wasm
    https://speakerdeck.com/tiran/
    

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29. Language Summit 2022: WASM Python, @ChristianHeimes, CC BY-SA 4.0
    linkedin.com/company/red-hat
    youtube.com/user/RedHatVideos
    facebook.com/redhatinc
    twitter.com/RedHat
    29
    Red Hat is the world’s leading provider of enterprise
    open source software solutions. Award-winning
    support, training, and consulting services make
    Red Hat a trusted adviser to the Fortune 500.
    Thank you
    

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