JavaScript API

Backward compatibility of the API is not guaranteed at this point.

Globals

Functions:

async loadPyodide(options)

Load the main Pyodide wasm module and initialize it.

async globalThis.loadPyodide(options)

Load the main Pyodide wasm module and initialize it.

Arguments:

• options.indexURL (string) – The URL from which Pyodide will load the main Pyodide runtime and packages. It is recommended that you leave this unchanged, providing an incorrect value can cause broken behavior. Default: The url that Pyodide is loaded from with the file name (pyodide.js or pyodide.mjs) removed.

• options.packageCacheDir (string) – The file path where packages will be cached in node. If a package exists in packageCacheDir it is loaded from there, otherwise it is downloaded from the JsDelivr CDN and then cached into packageCacheDir. Only applies when running in node; ignored in browsers. Default: same as indexURL

• options.lockFileURL (string) – The URL from which Pyodide will load the Pyodide pyodide-lock.json lock file. You can produce custom lock files with micropip.freeze(). Default: `${indexURL}/pyodide-lock.json`

• options.fullStdLib (boolean) – Load the full Python standard library. Setting this to false excludes unvendored modules from the standard library. Default: false

• options.stdLibURL (string) – The URL from which to load the standard library python_stdlib.zip file. This URL includes the most of the Python standard library. Some stdlib modules were unvendored, and can be loaded separately with fullStdLib: true option or by their package name. Default: `${indexURL}/python_stdlib.zip`

• options.stdin (() => string) – Override the standard input callback. Should ask the user for one line of input. The pyodide.setStdin() function is more flexible and should be preferred.

• options.stdout ((msg: string) => void) – Override the standard output callback. The pyodide.setStdout() function is more flexible and should be preferred in most cases, but depending on the args passed to loadPyodide, Pyodide may write to stdout on startup, which can only be controlled by passing a custom stdout function.

• options.stderr ((msg: string) => void) – Override the standard error output callback. The pyodide.setStderr() function is more flexible and should be preferred in most cases, but depending on the args passed to loadPyodide, Pyodide may write to stdout on startup, which can only be controlled by passing a custom stdout function.

• options.jsglobals (object) – The object that Pyodide will use for the js module. Default: globalThis

• options.args (string[]) – Command line arguments to pass to Python on startup. See Python command line interface options for more details. Default: []

• options.env ({ [key: string]: string; }) – Environment variables to pass to Python. This can be accessed inside of Python at runtime via os.environ. Certain environment variables change the way that Python loads: https://docs.python.org/3.10/using/cmdline.html#environment-variables Default: {}. If env.HOME is undefined, it will be set to a default value of "/home/pyodide"

• options.packages (string[]) – A list of packages to load as Pyodide is initializing. This is the same as loading the packages with pyodide.loadPackage() after Pyodide is loaded except using the packages option is more efficient because the packages are downloaded while Pyodide bootstraps itself.

• options.pyproxyToStringRepr (boolean) – Opt into the old behavior where PyProxy.toString() calls repr() and not str().

• options.enableRunUntilComplete (boolean) – Make loop.run_until_complete() function correctly using stack switching

• options.checkAPIVersion (boolean) – If true (default), throw an error if the version of Pyodide core does not match the version of the Pyodide js package.

Returns:

Promise<typeof PyodideAPI> – The pyodide module.

Example

async function main() {
  const pyodide = await loadPyodide({
    fullStdLib: true,
    stdout: (msg) => console.log(`Pyodide: ${msg}`),
  });
  console.log("Loaded Pyodide");
}
main();

pyodide

Type Aliases:

TypedArray

Interfaces:

PackageData

Attributes:

ERRNO_CODES	A map from posix error names to error codes.
FS	An alias to the Emscripten File System API.
PATH	An alias to the Emscripten Path API.
canvas	APIs to set a canvas for rendering graphics.
ffi	Foreign function interface classes.
globals	An alias to the global Python namespace.
loadedPackages	An object whose keys are the names of the loaded packages and whose values are the install sources of the packages.
pyodide_py	An alias to the Python pyodide package.
version	The Pyodide version.

Functions:

checkInterrupt()	Throws a KeyboardInterrupt error if a KeyboardInterrupt has been requested via the interrupt buffer.
async loadPackage(names, options)	Load packages from the Pyodide distribution or Python wheels by URL.
async loadPackagesFromImports(code, options)	Inspect a Python code chunk and use pyodide.loadPackage() to install any known packages that the code chunk imports.
makeMemorySnapshot(param0={})
async mountNativeFS(path, fileSystemHandle)	Mounts a FileSystemDirectoryHandle into the target directory.
mountNodeFS(emscriptenPath, hostPath)	Mounts a host directory into Pyodide file system.
pyimport(mod_name)	Imports a module and returns it.
registerComlink(Comlink)	Tell Pyodide about Comlink.
registerJsModule(name, module)	Registers the JavaScript object module as a JavaScript module named name.
runPython(code, options)	Runs a string of Python code from JavaScript, using eval_code() to evaluate the code.
async runPythonAsync(code, options)	Run a Python code string with top level await using eval_code_async() to evaluate the code.
scheduleCallback(callback, timeout=0)	Schedule a callback.
setDebug(debug)	Turn on or off debug mode.
setInterruptBuffer(interrupt_buffer)	Sets the interrupt buffer to be interrupt_buffer.
setStderr(options)	Sets the standard error handler.
setStdin(options)	Set a stdin handler.
setStdout(options)	Sets the standard out handler.
toPy(obj, options)	Convert a JavaScript object to a Python object as best as possible.
unpackArchive(buffer, format, options)	Unpack an archive into a target directory.
unregisterJsModule(name)	Unregisters a JavaScript module with given name that has been previously registered with pyodide.registerJsModule() or register_js_module().

pyodide.TypedArray

type: Int8Array | Uint8Array | Int16Array | Uint16Array | Int32Array | Uint32Array | Uint8ClampedArray | Float32Array | Float64Array

interface pyodide.PackageData

PackageData.fileName

type: string

PackageData.name

type: string

PackageData.packageType

type: “package” | “cpython_module” | “shared_library” | “static_library”

PackageData.version

type: string

pyodide.ERRNO_CODES

type: { [code: string]: number; }

A map from posix error names to error codes.

pyodide.FS

type: FS

An alias to the Emscripten File System API.

This provides a wide range of POSIX-like file/device operations, including mount which can be used to extend the in-memory filesystem with features like persistence.

While all the file systems implementations are enabled, only the default MEMFS is guaranteed to work in all runtime settings. The implementations are available as members of FS.filesystems: IDBFS, NODEFS, PROXYFS, WORKERFS.

pyodide.PATH

type: any

An alias to the Emscripten Path API.

This provides a variety of operations for working with file system paths, such as dirname, normalize, and splitPath.

pyodide.globals

type: PyProxy

An alias to the global Python namespace.

For example, to access a variable called foo in the Python global scope, use pyodide.globals.get("foo")

pyodide.loadedPackages

type: Record<string, string>

An object whose keys are the names of the loaded packages and whose values are the install sources of the packages. Use Object.keys(pyodide.loadedPackages) to get the list of names of loaded packages, and pyodide.loadedPackages[package_name] to access the install source for a particular package_name.

pyodide.pyodide_py

type: PyProxy

An alias to the Python pyodide package.

You can use this to call functions defined in the Pyodide Python package from JavaScript.

pyodide.version

type: string

The Pyodide version.

The version here is a Python version, following PEP 440. This is different from the version in package.json which follows the node package manager version convention.

pyodide.checkInterrupt()

Throws a KeyboardInterrupt error if a KeyboardInterrupt has been requested via the interrupt buffer.

This can be used to enable keyboard interrupts during execution of JavaScript code, just as PyErr_CheckSignals() is used to enable keyboard interrupts during execution of C code.

async pyodide.loadPackage(names, options)

Load packages from the Pyodide distribution or Python wheels by URL.

This installs packages in the virtual filesystem. Packages needs to be imported from Python before it can be used.

This function can only install packages included in the Pyodide distribution, or Python wheels by URL, without dependency resolution. It is significantly more limited in terms of functionality as compared to micropip, however it has less overhead and can be faster.

When installing binary wheels by URLs it is user’s responsibility to check that the installed binary wheel is compatible in terms of Python and Emscripten versions. Compatibility is not checked during installation time (unlike with micropip). If a wheel for the wrong Python/Emscripten version is installed it would fail at import time.

Arguments:

• names (string | string[] | PyProxy) – Either a single package name or URL or a list of them. URLs can be absolute or relative. The URLs must correspond to Python wheels: either pure Python wheels, with a file name ending with none-any.whl or Emscripten/WASM 32 wheels, with a file name ending with cp<pyversion>_emscripten_<em_version>_wasm32.whl. The argument can be a PyProxy of a list, in which case the list will be converted to JavaScript and the PyProxy will be destroyed.

• options.messageCallback ((message: string) => void) – A callback, called with progress messages (optional)

• options.errorCallback ((message: string) => void) – A callback, called with error/warning messages (optional)

• options.checkIntegrity (boolean) – If true, check the integrity of the downloaded packages (default: true)

Returns:

Promise<PackageData[]> – The loaded package data.

async pyodide.loadPackagesFromImports(code, options)

Inspect a Python code chunk and use pyodide.loadPackage() to install any known packages that the code chunk imports. Uses the Python API pyodide.code.find_imports() to inspect the code.

For example, given the following code as input

import numpy as np
x = np.array([1, 2, 3])

loadPackagesFromImports() will call pyodide.loadPackage(['numpy']).

Arguments:

• code (string) – The code to inspect.

• options.messageCallback ((message: string) => void) – A callback, called with progress messages (optional)

• options.errorCallback ((message: string) => void) – A callback, called with error/warning messages (optional)

• options.checkIntegrity (boolean) – If true, check the integrity of the downloaded packages (default: true)

Returns:

Promise<PackageData[]>

pyodide.makeMemorySnapshot(param0={})

Arguments:

• param0 ({ serializer?: (obj: any) => any; })

Returns:

Uint8Array

async pyodide.mountNativeFS(path, fileSystemHandle)

Mounts a FileSystemDirectoryHandle into the target directory. Currently it’s only possible to acquire a FileSystemDirectoryHandle in Chrome.

Arguments:

• path (string) – The absolute path in the Emscripten file system to mount the native directory. If the directory does not exist, it will be created. If it does exist, it must be empty.

• fileSystemHandle (FileSystemDirectoryHandle) – A handle returned by navigator.storage.getDirectory() or window.showDirectoryPicker().

Returns:

Promise<{ syncfs: () => Promise<void>; }>

pyodide.mountNodeFS(emscriptenPath, hostPath)

Mounts a host directory into Pyodide file system. Only works in node.

Arguments:

• emscriptenPath (string) – The absolute path in the Emscripten file system to mount the native directory. If the directory does not exist, it will be created. If it does exist, it must be empty.

• hostPath (string) – The host path to mount. It must be a directory that exists.

pyodide.pyimport(mod_name)

Imports a module and returns it.

If name has no dot in it, then pyimport(name) is approximately equivalent to:

pyodide.runPython(`import ${name}; ${name}`)

except that name is not introduced into the Python global namespace. If the name has one or more dots in it, say it is of the form path.name where name has no dots but path may have zero or more dots. Then it is approximately the same as:

pyodide.runPython(`from ${path} import ${name}; ${name}`);

Arguments:

• mod_name (string) – The name of the module to import

Returns:

any

Example

pyodide.pyimport("math.comb")(4, 2) // returns 4 choose 2 = 6

pyodide.registerComlink(Comlink)

Tell Pyodide about Comlink. Necessary to enable importing Comlink proxies into Python.

Arguments:

• Comlink (any)

pyodide.registerJsModule(name, module)

Registers the JavaScript object module as a JavaScript module named name. This module can then be imported from Python using the standard Python import system. If another module by the same name has already been imported, this won’t have much effect unless you also delete the imported module from sys.modules. This calls register_js_module().

Any attributes of the JavaScript objects which are themselves objects will be treated as submodules:

pyodide.registerJsModule("mymodule", { submodule: { value: 7 } });
pyodide.runPython(`
    from mymodule.submodule import value
    assert value == 7
`);

If you wish to prevent this, try the following instead:

const sys = pyodide.pyimport("sys");
sys.modules.set("mymodule", { obj: { value: 7 } });
pyodide.runPython(`
    from mymodule import obj
    assert obj.value == 7
    # attempting to treat obj as a submodule raises ModuleNotFoundError:
    # "No module named 'mymodule.obj'; 'mymodule' is not a package"
    from mymodule.obj import value
`);

Arguments:

• name (string) – Name of the JavaScript module to add

• module (object) – JavaScript object backing the module

pyodide.runPython(code, options)

Runs a string of Python code from JavaScript, using eval_code() to evaluate the code. If the last statement in the Python code is an expression (and the code doesn’t end with a semicolon), the value of the expression is returned.

Arguments:

• code (string) – The Python code to run

• options.globals (PyProxy) – An optional Python dictionary to use as the globals. Defaults to pyodide.globals.

• options.locals (PyProxy) – An optional Python dictionary to use as the locals. Defaults to the same as globals.

• options.filename (string) – An optional string to use as the file name. Defaults to "<exec>". If a custom file name is given, the traceback for any exception that is thrown will show source lines (unless the given file name starts with < and ends with >).

Returns:

any – The result of the Python code translated to JavaScript. See the documentation for eval_code() for more info.

Example

async function main(){
  const pyodide = await loadPyodide();
  console.log(pyodide.runPython("1 + 2"));
  // 3

  const globals = pyodide.toPy({ x: 3 });
  console.log(pyodide.runPython("x + 1", { globals }));
  // 4

  const locals = pyodide.toPy({ arr: [1, 2, 3] });
  console.log(pyodide.runPython("sum(arr)", { locals }));
  // 6
}
main();

async pyodide.runPythonAsync(code, options)

Run a Python code string with top level await using eval_code_async() to evaluate the code. Returns a promise which resolves when execution completes. If the last statement in the Python code is an expression (and the code doesn’t end with a semicolon), the returned promise will resolve to the value of this expression.

For example:

let result = await pyodide.runPythonAsync(`
    from js import fetch
    response = await fetch("./pyodide-lock.json")
    packages = await response.json()
    # If final statement is an expression, its value is returned to JavaScript
    len(packages.packages.object_keys())
`);
console.log(result); // 79

Python imports

Since pyodide 0.18.0, you must call loadPackagesFromImports() to import any python packages referenced via import statements in your code. This function will no longer do it for you.

Arguments:

• code (string) – The Python code to run

• options.globals (PyProxy) – An optional Python dictionary to use as the globals. Defaults to pyodide.globals.

• options.locals (PyProxy) – An optional Python dictionary to use as the locals. Defaults to the same as globals.

• options.filename (string) – An optional string to use as the file name. Defaults to "<exec>". If a custom file name is given, the traceback for any exception that is thrown will show source lines (unless the given file name starts with < and ends with >).

Returns:

Promise<any> – The result of the Python code translated to JavaScript.

pyodide.scheduleCallback(callback, timeout=0)

Schedule a callback. Supports both immediate and delayed callbacks.

Arguments:

• callback (() => void) – The callback to be scheduled

• timeout (number) – The delay in milliseconds before the callback is called

pyodide.setDebug(debug)

Turn on or off debug mode. In debug mode, some error messages are improved at a performance cost.

Arguments:

• debug (boolean) – If true, turn debug mode on. If false, turn debug mode off.

Returns:

boolean – The old value of the debug flag.

pyodide.setInterruptBuffer(interrupt_buffer)

Sets the interrupt buffer to be interrupt_buffer. This is only useful when Pyodide is used in a webworker. The buffer should be a SharedArrayBuffer shared with the main browser thread (or another worker). In that case, signal signum may be sent by writing signum into the interrupt buffer. If signum does not satisfy 0 < signum < 65 it will be silently ignored.

You can disable interrupts by calling setInterruptBuffer(undefined).

If you wish to trigger a KeyboardInterrupt, write SIGINT (a 2) into the interrupt buffer.

By default SIGINT raises a KeyboardInterrupt and all other signals are ignored. You can install custom signal handlers with the signal module. Even signals that normally have special meaning and can’t be overridden like SIGKILL and SIGSEGV are ignored by default and can be used for any purpose you like.

Arguments:

• interrupt_buffer (TypedArray)

pyodide.setStderr(options)

Sets the standard error handler. See the documentation for pyodide.setStdout().

Arguments:

• options.batched ((output: string) => void)

• options.raw ((charCode: number) => void)

• options.write ((buffer: Uint8Array) => number)

• options.isatty (boolean)

pyodide.setStdin(options)

Set a stdin handler. See redirecting standard streams for a more detailed explanation. There are two different possible interfaces to implement a handler. It’s also possible to select either the default handler or an error handler that always returns an IO error.

1. passing a read function (see below),

2. passing a stdin function (see below),

3. passing error: true indicates that attempting to read from stdin should always raise an IO error.

4. passing none of these sets the default behavior. In node, the default is to read from stdin. In the browser, the default is to raise an error.

The functions on the options argument will be called with options bound to this so passing an instance of a class as the options object works as expected.

The interfaces that the handlers implement are as follows:

1. The read function is called with a Uint8Array argument. The function should place the utf8-encoded input into this buffer and return the number of bytes written. For instance, if the buffer was completely filled with input, then return buffer.length. If a read function is passed you may optionally also pass an fsync function which is called when stdin is flushed.

2. The stdin function is called with zero arguments. It should return one of:

   • null or undefined: these are interpreted as end of file.

   • a number

   • a string

   • an ArrayBuffer or TypedArray with BYTES_PER_ELEMENT equal to 1. The buffer should contain utf8 encoded text.

   If a number is returned, it is interpreted as a single character code. The number should be between 0 and 255.

   If a string is returned, it is encoded into a buffer using TextEncoder. By default, an EOF is appended after each string or buffer returned. If this behavior is not desired, pass autoEOF: false.

Arguments:

• options.stdin (() => null | undefined | string | ArrayBuffer | Uint8Array | number) – A stdin handler

• options.read ((buffer: Uint8Array) => number) – A read handler

• options.error (boolean) – If this is set to true, attempts to read from stdin will always set an IO error.

• options.isatty (boolean) – Should isatty(stdin) be true or false (default false).

• options.autoEOF (boolean) – Insert an EOF automatically after each string or buffer? (default true). This option can only be used with the stdin handler.

pyodide.setStdout(options)

Sets the standard out handler. A batched handler, a raw handler, or a write function can be provided. If no handler is provided, we restore the default handler.

The functions on the options argument will be called with options bound to this so passing an instance of a class as the options object works as expected.

Arguments:

• options.batched ((output: string) => void) – A batched handler is called with a string whenever a newline character is written or stdout is flushed. In the former case, the received line will end with a newline, in the latter case it will not.

• options.raw ((charCode: number) => void) – A raw handler is called with the handler is called with a number for each byte of the output to stdout.

• options.write ((buffer: Uint8Array) => number) – A write handler is called with a buffer that contains the utf8 encoded binary data

• options.isatty (boolean) – Should isatty(stdout) return true or false. Must be false if a batched handler is used. (default false).

Example

async function main(){
  const pyodide = await loadPyodide();
  pyodide.setStdout({ batched: (msg) => console.log(msg) });
  pyodide.runPython("print('ABC')");
  // 'ABC'
  pyodide.setStdout({ raw: (byte) => console.log(byte) });
  pyodide.runPython("print('ABC')");
  // 65
  // 66
  // 67
  // 10 (the ascii values for 'ABC' including a new line character)
}
main();

pyodide.toPy(obj, options)

Convert a JavaScript object to a Python object as best as possible.

This is similar to to_py() but for use from JavaScript. If the object is immutable or a PyProxy, it will be returned unchanged. If the object cannot be converted into Python, it will be returned unchanged.

See JavaScript to Python for more information.

Arguments:

• obj (any) – The object to convert.

• options.depth (number) – Optional argument to limit the depth of the conversion.

• options.defaultConverter ((value: any, converter: (value: any) => any, cacheConversion: (input: any, output: any) => void) => any) – Optional argument to convert objects with no default conversion. See the documentation of to_py().

Returns:

any – The object converted to Python.

pyodide.unpackArchive(buffer, format, options)

Unpack an archive into a target directory.

Arguments:

• buffer (ArrayBuffer | TypedArray) – The archive as an ArrayBuffer or TypedArray.

• format (string) – The format of the archive. Should be one of the formats recognized by shutil.unpack_archive(). By default the options are 'bztar', 'gztar', 'tar', 'zip', and 'wheel'. Several synonyms are accepted for each format, e.g., for 'gztar' any of '.gztar', '.tar.gz', '.tgz', 'tar.gz' or 'tgz' are considered to be synonyms.

• options.extractDir (string) – The directory to unpack the archive into. Defaults to the working directory.

pyodide.unregisterJsModule(name)

Unregisters a JavaScript module with given name that has been previously registered with pyodide.registerJsModule() or register_js_module(). If a JavaScript module with that name does not already exist, will throw an error. Note that if the module has already been imported, this won’t have much effect unless you also delete the imported module from sys.modules. This calls unregister_js_module().

Arguments:

• name (string) – Name of the JavaScript module to remove

pyodide.ffi

Foreign function interface classes. Can be used for typescript type annotations or at runtime for instanceof checks.

To import types from pyodide.ffi you can use for example

import type { PyProxy } from "pyodide/ffi";

If you want to do an instance check, you’ll need to access the type via the Pyodide API returned from loadPyodide():

const pyodide = loadPyodide();
const result = pyodide.runPython("... code here");
if (result instanceof pyodide.ffi.PyProxy) {
  // Do something
}

Classes:

PyAsyncGenerator	A PyProxy whose proxied Python object is an asynchronous generator (i.e., it is an instance of AsyncGenerator)
PyAsyncIterable	A PyProxy whose proxied Python object is asynchronous iterable (i.e., has an __aiter__() method).
PyAsyncIterator	A PyProxy whose proxied Python object is an asynchronous iterator
PyAwaitable	A PyProxy whose proxied Python object is awaitable (i.e., has an __await__() method).
PyBuffer	A PyProxy whose proxied Python object supports the Python Buffer Protocol.
PyBufferView	A class to allow access to Python data buffers from JavaScript.
PyCallable	A PyProxy whose proxied Python object is callable (i.e., has an __call__() method).
PyDict	A PyProxy whose proxied Python object is a dict.
PyGenerator	A PyProxy whose proxied Python object is a generator (i.e., it is an instance of Generator).
PyIterable	A PyProxy whose proxied Python object is iterable (i.e., it has an __iter__() method).
PyIterator	A PyProxy whose proxied Python object is an iterator (i.e., has a send() or __next__() method).
PyMutableSequence	A PyProxy whose proxied Python object is an MutableSequence (i.e., a list)
PyProxy	A PyProxy is an object that allows idiomatic use of a Python object from JavaScript.
PyProxyWithGet	A PyProxy whose proxied Python object has a __getitem__() method.
PyProxyWithHas	A PyProxy whose proxied Python object has a __contains__() method.
PyProxyWithLength	A PyProxy whose proxied Python object has a __len__() method.
PyProxyWithSet	A PyProxy whose proxied Python object has a __setitem__() or __delitem__() method.
PySequence	A PyProxy whose proxied Python object is an Sequence (i.e., a list)
PythonError	A JavaScript error caused by a Python exception.

class pyodide.ffi.PyAsyncGenerator()

A PyProxy whose proxied Python object is an asynchronous generator (i.e., it is an instance of AsyncGenerator)

Extends:

• PyProxy

async PyAsyncGenerator.return(v)

Throws a GeneratorExit into the generator and if the GeneratorExit is not caught returns the argument value {done: true, value: v}. If the generator catches the GeneratorExit and returns or yields another value the next value of the generator this is returned in the normal way. If it throws some error other than GeneratorExit or StopAsyncIteration, that error is propagated. See the documentation for AsyncGenerator.throw()

Arguments:

• v (any) – The value to return from the generator.

Returns:

Promise<IteratorResult<any, any>> – An Object with two properties: done and value. When the generator yields some_value, return returns {done : false, value : some_value}. When the generator raises a StopAsyncIteration exception, return returns {done : true, value : result_value}.

async PyAsyncGenerator.throw(exc)

Throws an exception into the Generator.

See the documentation for AsyncGenerator.throw().

Arguments:

• exc (any) – Error The error to throw into the generator. Must be an instanceof Error.

Returns:

Promise<IteratorResult<any, any>> – An Object with two properties: done and value. When the generator yields some_value, return returns {done : false, value : some_value}. When the generator raises a StopIteration(result_value) exception, return returns {done : true, value : result_value}.

class pyodide.ffi.PyAsyncIterable()

A PyProxy whose proxied Python object is asynchronous iterable (i.e., has an __aiter__() method).

Extends:

• PyProxy

PyAsyncIterable.[Symbol․asyncIterator]()

This translates to the Python code aiter(obj). Return an async iterator associated to the proxy. See the documentation for Symbol.asyncIterator.

This will be used implicitly by for(await let x of proxy){}.

Returns:

AsyncIterator

class pyodide.ffi.PyAsyncIterator()

A PyProxy whose proxied Python object is an asynchronous iterator

Extends:

• PyProxy

async PyAsyncIterator.next(arg=undefined)

This translates to the Python code anext(obj). Returns the next value of the asynchronous iterator. The argument will be sent to the Python iterator (if it’s a generator for instance).

This will be used implicitly by for(let x of proxy){}.

Arguments:

• arg (any) – The value to send to a generator. The value will be assigned as a result of a yield expression.

Returns:

Promise<IteratorResult<any, any>> – An Object with two properties: done and value. When the iterator yields some_value, next returns {done : false, value : some_value}. When the giterator is done, next returns {done : true }.

class pyodide.ffi.PyAwaitable()

A PyProxy whose proxied Python object is awaitable (i.e., has an __await__() method).

Extends:

• PyProxy

• Promise<any>

async PyAwaitable.catch<TResult>(onrejected)

Attaches a callback for only the rejection of the Promise.

Type parameters:

TResult –

Arguments:

• onrejected (null | (reason: any) => TResult | PromiseLike<TResult>) – The callback to execute when the Promise is rejected.

Returns:

Promise<any> – A Promise for the completion of the callback.

async PyAwaitable.finally(onfinally)

Attaches a callback that is invoked when the Promise is settled (fulfilled or rejected). The resolved value cannot be modified from the callback.

Arguments:

• onfinally (null | () => void) – The callback to execute when the Promise is settled (fulfilled or rejected).

Returns:

Promise<any> – A Promise for the completion of the callback.

async PyAwaitable.then<TResult1, TResult2>(onfulfilled, onrejected)

Attaches callbacks for the resolution and/or rejection of the Promise.

Type parameters:

• TResult1 –

• TResult2 –

Arguments:

• onfulfilled (null | (value: any) => TResult1 | PromiseLike<TResult1>) – The callback to execute when the Promise is resolved.

• onrejected (null | (reason: any) => TResult2 | PromiseLike<TResult2>) – The callback to execute when the Promise is rejected.

Returns:

Promise<TResult1 | TResult2> – A Promise for the completion of which ever callback is executed.

class pyodide.ffi.PyBuffer()

A PyProxy whose proxied Python object supports the Python Buffer Protocol.

Examples of buffers include {py:class}`bytes` objects and numpy {external+numpy:ref}`arrays`.

Extends:

• PyProxy

PyBuffer.getBuffer(type)

Get a view of the buffer data which is usable from JavaScript. No copy is ever performed.

We do not support suboffsets, if the buffer requires suboffsets we will throw an error. JavaScript nd array libraries can’t handle suboffsets anyways. In this case, you should use the toJs() api or copy the buffer to one that doesn’t use suboffsets (using e.g., numpy.ascontiguousarray()).

If the buffer stores big endian data or half floats, this function will fail without an explicit type argument. For big endian data you can use toJs(). DataView has support for big endian data, so you might want to pass 'dataview' as the type argument in that case.

Arguments:

• type (string) – The type of the data field in the output. Should be one of: "i8", "u8", "u8clamped", "i16", "u16", "i32", "u32", "i32", "u32", "i64", "u64", "f32", "f64", or "dataview". This argument is optional, if absent getBuffer() will try to determine the appropriate output type based on the buffer format string (see Format Strings).

Returns:

PyBufferView

class pyodide.ffi.PyBufferView()

A class to allow access to Python data buffers from JavaScript. These are produced by getBuffer() and cannot be constructed directly. When you are done, release it with the release() method. See the Python Buffer Protocol documentation for more information.

To find the element x[a_1, ..., a_n], you could use the following code:

function multiIndexToIndex(pybuff, multiIndex) {
  if (multindex.length !== pybuff.ndim) {
    throw new Error("Wrong length index");
  }
  let idx = pybuff.offset;
  for (let i = 0; i < pybuff.ndim; i++) {
    if (multiIndex[i] < 0) {
      multiIndex[i] = pybuff.shape[i] - multiIndex[i];
    }
    if (multiIndex[i] < 0 || multiIndex[i] >= pybuff.shape[i]) {
      throw new Error("Index out of range");
    }
    idx += multiIndex[i] * pybuff.stride[i];
  }
  return idx;
}
console.log("entry is", pybuff.data[multiIndexToIndex(pybuff, [2, 0, -1])]);

Converting between TypedArray types

The following naive code to change the type of a typed array does not work:

// Incorrectly convert a TypedArray.
// Produces a Uint16Array that points to the entire WASM memory!
let myarray = new Uint16Array(buffer.data.buffer);

Instead, if you want to convert the output TypedArray, you need to say:

// Correctly convert a TypedArray.
let myarray = new Uint16Array(
    buffer.data.buffer,
    buffer.data.byteOffset,
    buffer.data.byteLength
);

PyBufferView.c_contiguous

type: boolean

Is it C contiguous? See memoryview.c_contiguous.

PyBufferView.data

type: TypedArray

The actual data. A typed array of an appropriate size backed by a segment of the WASM memory.

The type argument of getBuffer() determines which sort of TypedArray or DataView to return. By default getBuffer() will look at the format string to determine the most appropriate option. Most often the result is a Uint8Array.

Contiguity

If the buffer is not contiguous, the readonly TypedArray will contain data that is not part of the buffer. Modifying this data leads to undefined behavior.

Read only buffers

If buffer.readonly is true, you should not modify the buffer. Modifying a read only buffer leads to undefined behavior.

PyBufferView.f_contiguous

type: boolean

Is it Fortran contiguous? See memoryview.f_contiguous.

PyBufferView.format

type: string

The format string for the buffer. See Format Strings and memoryview.format.

PyBufferView.itemsize

type: number

How large is each entry in bytes? See memoryview.itemsize.

PyBufferView.nbytes

type: number

The total number of bytes the buffer takes up. This is equal to buff.data.byteLength. See memoryview.nbytes.

PyBufferView.ndim

type: number

The number of dimensions of the buffer. If ndim is 0, the buffer represents a single scalar or struct. Otherwise, it represents an array. See memoryview.ndim.

PyBufferView.offset

type: number

The offset of the first entry of the array. For instance if our array is 3d, then you will find array[0,0,0] at pybuf.data[pybuf.offset]

PyBufferView.readonly

type: boolean

If the data is read only, you should not modify it. There is no way for us to enforce this, but it may cause very weird behavior. See memoryview.readonly.

PyBufferView.shape

type: number[]

The shape of the buffer, that is how long it is in each dimension. The length will be equal to ndim. For instance, a 2x3x4 array would have shape [2, 3, 4]. See memoryview.shape.

PyBufferView.strides

type: number[]

An array of of length ndim giving the number of elements to skip to get to a new element in each dimension. See the example definition of a multiIndexToIndex function above. See memoryview.strides.

PyBufferView.release()

Release the buffer. This allows the memory to be reclaimed.

class pyodide.ffi.PyCallable()

A PyProxy whose proxied Python object is callable (i.e., has an __call__() method).

Extends:

• PyProxy

PyCallable.apply(thisArg, jsargs)

The apply() method calls the specified function with a given this value, and arguments provided as an array (or an array-like object). Like Function.apply().

Arguments:

• thisArg (any) – The this argument. Has no effect unless the PyCallable has captureThis() set. If captureThis() is set, it will be passed as the first argument to the Python function.

• jsargs (any) – The array of arguments

Returns:

any – The result from the function call.

PyCallable.bind(thisArg, ...jsargs)

The bind() method creates a new function that, when called, has its this keyword set to the provided value, with a given sequence of arguments preceding any provided when the new function is called. See Function.bind().

If the PyCallable does not have captureThis() set, the this parameter will be discarded. If it does have captureThis() set, thisArg will be set to the first argument of the Python function. The returned proxy and the original proxy have the same lifetime so destroying either destroys both.

Arguments:

• thisArg (any) – The value to be passed as the this parameter to the target function func when the bound function is called.

• jsargs (any) – Extra arguments to prepend to arguments provided to the bound function when invoking func.

Returns:

PyProxy

PyCallable.call(thisArg, ...jsargs)

Calls the function with a given this value and arguments provided individually. See Function.call().

Arguments:

• thisArg (any) – The this argument. Has no effect unless the PyCallable has captureThis() set. If captureThis() is set, it will be passed as the first argument to the Python function.

• jsargs (any) – The arguments

Returns:

any – The result from the function call.

PyCallable.callKwargs(...jsargs)

Call the function with keyword arguments. The last argument must be an object with the keyword arguments.

Arguments:

• jsargs (any)

Returns:

any

PyCallable.callKwargsRelaxed(...jsargs)

Call the function with keyword arguments in a “relaxed” manner. The last argument must be an object with the keyword arguments. Any extra arguments will be ignored. This matches the behavior of JavaScript functions more accurately.

Missing arguments are NOT filled with None. If too few arguments are passed, this will still raise a TypeError. Also, if the same argument is passed as both a keyword argument and a positional argument, it will raise an error.

This uses pyodide.code.relaxed_call().

Arguments:

• jsargs (any)

Returns:

any

async PyCallable.callPromising(...jsargs)

Call the function with stack switching enabled. The last argument must be an object with the keyword arguments. Functions called this way can use run_sync() to block until an Awaitable is resolved. Only works in runtimes with JS Promise integration.

Experimental

This feature is not yet stable.

Arguments:

• jsargs (any)

Returns:

Promise<any>

async PyCallable.callPromisingKwargs(...jsargs)

Call the function with stack switching enabled. The last argument must be an object with the keyword arguments. Functions called this way can use run_sync() to block until an Awaitable is resolved. Only works in runtimes with JS Promise integration.

Experimental

This feature is not yet stable.

Arguments:

• jsargs (any)

Returns:

Promise<any>

PyCallable.callRelaxed(...jsargs)

Call the function in a “relaxed” manner. Any extra arguments will be ignored. This matches the behavior of JavaScript functions more accurately.

Any extra arguments will be ignored. This matches the behavior of JavaScript functions more accurately. Missing arguments are NOT filled with None. If too few arguments are passed, this will still raise a TypeError.

This uses pyodide.code.relaxed_call().

Arguments:

• jsargs (any)

Returns:

any

PyCallable.callWithOptions(options, ...jsargs)

Call the Python function. The first parameter controls various parameters that change the way the call is performed.

Arguments:

• options.relaxed (boolean) – If true, extra arguments are ignored instead of raising a TypeError.

• options.kwargs (boolean) – If true, the last argument is treated as a collection of keyword arguments.

• options.promising (boolean) – If true, the call is made with stack switching enabled. Not needed if the callee is an async Python function.

• jsargs (any) – Arguments to the Python function.

Returns:

any

PyCallable.captureThis()

Returns a PyProxy that passes this as the first argument to the Python function. The returned PyProxy has the internal captureThis property set.

It can then be used as a method on a JavaScript object. The returned proxy and the original proxy have the same lifetime so destroying either destroys both.

For example:

let obj = { a : 7 };
pyodide.runPython(`
  def f(self):
    return self.a
`);
// Without captureThis, it doesn't work to use f as a method for obj:
obj.f = pyodide.globals.get("f");
obj.f(); // raises "TypeError: f() missing 1 required positional argument: 'self'"
// With captureThis, it works fine:
obj.f = pyodide.globals.get("f").captureThis();
obj.f(); // returns 7

Returns:

PyProxy – The resulting PyProxy. It has the same lifetime as the original PyProxy but passes this to the wrapped function.

class pyodide.ffi.PyDict()

A PyProxy whose proxied Python object is a dict.

Extends:

• PyProxy

• PyProxyWithGet

• PyProxyWithSet

• PyProxyWithHas

• PyProxyWithLength

• PyIterable

class pyodide.ffi.PyGenerator()

A PyProxy whose proxied Python object is a generator (i.e., it is an instance of Generator).

Extends:

• PyProxy

PyGenerator.return(v)

Throws a GeneratorExit into the generator and if the GeneratorExit is not caught returns the argument value {done: true, value: v}. If the generator catches the GeneratorExit and returns or yields another value the next value of the generator this is returned in the normal way. If it throws some error other than GeneratorExit or StopIteration, that error is propagated. See the documentation for Generator.return().

Arguments:

• v (any) – The value to return from the generator.

Returns:

IteratorResult<any, any> – An Object with two properties: done and value. When the generator yields some_value, return returns {done : false, value : some_value}. When the generator raises a StopIteration(result_value) exception, return returns {done : true, value : result_value}.

PyGenerator.throw(exc)

Throws an exception into the Generator.

See the documentation for Generator.throw().

Arguments:

• exc (any) – Error The error to throw into the generator. Must be an instanceof Error.

Returns:

IteratorResult<any, any> – An Object with two properties: done and value. When the generator yields some_value, return returns {done : false, value : some_value}. When the generator raises a StopIteration(result_value) exception, return returns {done : true, value : result_value}.

class pyodide.ffi.PyIterable()

A PyProxy whose proxied Python object is iterable (i.e., it has an __iter__() method).

Extends:

• PyProxy

PyIterable.[Symbol․iterator]()

This translates to the Python code iter(obj). Return an iterator associated to the proxy. See the documentation for Symbol.iterator.

This will be used implicitly by for(let x of proxy){}.

Returns:

Iterator

class pyodide.ffi.PyIterator()

A PyProxy whose proxied Python object is an iterator (i.e., has a send() or __next__() method).

Extends:

• PyProxy

PyIterator.next(arg=undefined)

This translates to the Python code next(obj). Returns the next value of the generator. See the documentation for Generator.next() The argument will be sent to the Python generator.

This will be used implicitly by for(let x of proxy){}.

Arguments:

• arg (any) – The value to send to the generator. The value will be assigned as a result of a yield expression.

Returns:

IteratorResult<any, any> – An Object with two properties: done and value. When the generator yields some_value, next returns {done : false, value : some_value}. When the generator raises a StopIteration exception, next returns {done : true, value : result_value}.

class pyodide.ffi.PyMutableSequence()

A PyProxy whose proxied Python object is an MutableSequence (i.e., a list)

Extends:

• PyProxy

PyMutableSequence.copyWithin(target, start, end)

The Array.copyWithin() method shallow copies part of a PyMutableSequence to another location in the same PyMutableSequence without modifying its length.

Arguments:

• target (number) – Zero-based index at which to copy the sequence to.

• start (number) – Zero-based index at which to start copying elements from.

• end (number) – Zero-based index at which to end copying elements from.

Returns:

any – The modified PyMutableSequence.

PyMutableSequence.fill(value, start, end)

The Array.fill() method changes all elements in an array to a static value, from a start index to an end index.

Arguments:

• value (any) – Value to fill the array with.

• start (number) – Zero-based index at which to start filling. Default 0.

• end (number) – Zero-based index at which to end filling. Default list.length.

Returns:

any

PyMutableSequence.pop()

The Array.pop() method removes the last element from a PyMutableSequence.

Returns:

any – The removed element from the PyMutableSequence; undefined if the PyMutableSequence is empty.

PyMutableSequence.push(...elts)

The Array.push() method adds the specified elements to the end of a PyMutableSequence.

Arguments:

• elts (any[]) – The element(s) to add to the end of the PyMutableSequence.

Returns:

any – The new length property of the object upon which the method was called.

PyMutableSequence.reverse()

The Array.reverse() method reverses a PyMutableSequence in place.

Returns:

PyMutableSequence – A reference to the same PyMutableSequence

PyMutableSequence.shift()

The Array.shift() method removes the first element from a PyMutableSequence.

Returns:

any – The removed element from the PyMutableSequence; undefined if the PyMutableSequence is empty.

PyMutableSequence.sort(compareFn)

The Array.sort() method sorts the elements of a PyMutableSequence in place.

Arguments:

• compareFn ((a: any, b: any) => number) – A function that defines the sort order.

Returns:

PyMutableSequence – A reference to the same PyMutableSequence

PyMutableSequence.splice(start, deleteCount, ...items)

The Array.splice() method changes the contents of a PyMutableSequence by removing or replacing existing elements and/or adding new elements in place.

Arguments:

• start (number) – Zero-based index at which to start changing the PyMutableSequence.

• deleteCount (number) – An integer indicating the number of elements in the PyMutableSequence to remove from start.

• items (any[]) – The elements to add to the PyMutableSequence, beginning from start.

Returns:

any[] – An array containing the deleted elements.

PyMutableSequence.unshift(...elts)

The Array.unshift() method adds the specified elements to the beginning of a PyMutableSequence.

Arguments:

• elts (any[]) – The elements to add to the front of the PyMutableSequence.

Returns:

any – The new length of the PyMutableSequence.

class pyodide.ffi.PyProxy()

A PyProxy is an object that allows idiomatic use of a Python object from JavaScript. See Proxying from Python into JavaScript.

PyProxy.type

type: readonly string

The name of the type of the object.

Usually the value is "module.name" but for builtins or interpreter-defined types it is just "name". As pseudocode this is:

ty = type(x)
if ty.__module__ == 'builtins' or ty.__module__ == "__main__":
    return ty.__name__
else:
    ty.__module__ + "." + ty.__name__

PyProxy.copy()

Make a new PyProxy pointing to the same Python object. Useful if the PyProxy is destroyed somewhere else.

Returns:

PyProxy

PyProxy.destroy(options)

Destroy the PyProxy. This will release the memory. Any further attempt to use the object will raise an error.

In a browser supporting FinalizationRegistry, Pyodide will automatically destroy the PyProxy when it is garbage collected, however there is no guarantee that the finalizer will be run in a timely manner so it is better to destroy the proxy explicitly.

Arguments:

• options.message (string) – The error message to print if use is attempted after destroying. Defaults to “Object has already been destroyed”.

• options.destroyRoundtrip (boolean)

PyProxy.toJs(options)

Converts the PyProxy into a JavaScript object as best as possible. By default does a deep conversion, if a shallow conversion is desired, you can use proxy.toJs({depth : 1}). See Explicit Conversion of PyProxy for more info.

Arguments:

• options.depth (number) – How many layers deep to perform the conversion. Defaults to infinite

• options.pyproxies (PyProxy[]) – If provided, toJs() will store all PyProxies created in this list. This allows you to easily destroy all the PyProxies by iterating the list without having to recurse over the generated structure. The most common use case is to create a new empty list, pass the list as pyproxies, and then later iterate over pyproxies to destroy all of created proxies.

• options.create_pyproxies (boolean) – If false, toJs() will throw a ConversionError rather than producing a PyProxy.

• options.dict_converter ((array: Iterable<[key: string, value: any]>) => any) – A function to be called on an iterable of pairs [key, value]. Convert this iterable of pairs to the desired output. For instance, Object.fromEntries() would convert the dict to an object, Array.from() converts it to an Array of pairs, and (it) => new Map(it) converts it to a Map (which is the default behavior).

• options.default_converter ((obj: PyProxy, convert: (obj: PyProxy) => any, cacheConversion: (obj: PyProxy, result: any) => void) => any) – Optional argument to convert objects with no default conversion. See the documentation of to_js().

Returns:

any – The JavaScript object resulting from the conversion.

PyProxy.toString()

Returns str(o) (unless pyproxyToStringRepr: true was passed to loadPyodide() in which case it will return repr(o))

Returns:

string

class pyodide.ffi.PyProxyWithGet()

A PyProxy whose proxied Python object has a __getitem__() method.

Extends:

• PyProxy

PyProxyWithGet.asJsJson()

Returns the object treated as a json adaptor.

With a JsonAdaptor:

1. property access / modification / deletion is implemented with __getitem__(), __setitem__(), and __delitem__() respectively.

2. If an attribute is accessed and the result implements __getitem__() then the result will also be a json adaptor.

For instance, JSON.stringify(proxy.asJsJson()) acts like an inverse to Python’s json.loads().

Returns:

PyProxy

PyProxyWithGet.get(key)

This translates to the Python code obj[key].

Arguments:

• key (any) – The key to look up.

Returns:

any – The corresponding value.

class pyodide.ffi.PyProxyWithHas()

A PyProxy whose proxied Python object has a __contains__() method.

Extends:

• PyProxy

PyProxyWithHas.has(key)

This translates to the Python code key in obj.

Arguments:

• key (any) – The key to check for.

Returns:

boolean – Is key present?

class pyodide.ffi.PyProxyWithLength()

A PyProxy whose proxied Python object has a __len__() method.

Extends:

• PyProxy

PyProxyWithLength.length

type: readonly number

The length of the object.

class pyodide.ffi.PyProxyWithSet()

A PyProxy whose proxied Python object has a __setitem__() or __delitem__() method.

Extends:

• PyProxy

PyProxyWithSet.delete(key)

This translates to the Python code del obj[key].

Arguments:

• key (any) – The key to delete.

PyProxyWithSet.set(key, value)

This translates to the Python code obj[key] = value.

Arguments:

• key (any) – The key to set.

• value (any) – The value to set it to.

class pyodide.ffi.PySequence()

A PyProxy whose proxied Python object is an Sequence (i.e., a list)

Extends:

• PyProxy

PySequence.asJsJson()

Returns the object treated as a json adaptor.

With a JsonAdaptor:

1. property access / modification / deletion is implemented with __getitem__(), __setitem__(), and __delitem__() respectively.

2. If an attribute is accessed and the result implements __getitem__() then the result will also be a json adaptor.

For instance, JSON.stringify(proxy.asJsJson()) acts like an inverse to Python’s json.loads().

Returns:

PyProxy

PySequence.at(index)

See Array.at(). Takes an integer value and returns the item at that index.

Arguments:

• index (number) – Zero-based index of the Sequence element to be returned, converted to an integer. Negative index counts back from the end of the Sequence.

Returns:

any – The element in the Sequence matching the given index.

PySequence.concat(...rest)

The Array.concat() method is used to merge two or more arrays. This method does not change the existing arrays, but instead returns a new array.

Arguments:

• rest (ConcatArray<any>[]) – Arrays and/or values to concatenate into a new array.

Returns:

any[] – A new Array instance.

PySequence.entries()

The Array.entries() method returns a new iterator object that contains the key/value pairs for each index in the Sequence.

Returns:

IterableIterator<[number, any]> – A new iterator object.

PySequence.every(predicate, thisArg)

See Array.every(). Tests whether every element in the Sequence passes the test implemented by the provided function.

Arguments:

• predicate ((value: any, index: number, array: any[]) => unknown) – A function to execute for each element in the Sequence. It should return a truthy value to indicate the element passes the test, and a falsy value otherwise.

• thisArg (any) – A value to use as this when executing predicate.

Returns:

boolean

PySequence.filter(predicate, thisArg)

See Array.filter(). Creates a shallow copy of a portion of a given Sequence, filtered down to just the elements from the given array that pass the test implemented by the provided function.

Arguments:

• predicate ((elt: any, index: number, array: any) => boolean) – A function to execute for each element in the array. It should return a truthy value to keep the element in the resulting array, and a falsy value otherwise.

• thisArg (any) – A value to use as this when executing predicate.

Returns:

any[]

PySequence.find(predicate, thisArg)

The Array.find() method returns the first element in the provided array that satisfies the provided testing function.

Arguments:

• predicate ((value: any, index: number, obj: any[]) => any) – A function to execute for each element in the Sequence. It should return a truthy value to indicate a matching element has been found, and a falsy value otherwise.

• thisArg (any) – A value to use as this when executing predicate.

Returns:

any – The first element in the Sequence that satisfies the provided testing function.

PySequence.findIndex(predicate, thisArg)

The Array.findIndex() method returns the index of the first element in the provided array that satisfies the provided testing function.

Arguments:

• predicate ((value: any, index: number, obj: any[]) => any) – A function to execute for each element in the Sequence. It should return a truthy value to indicate a matching element has been found, and a falsy value otherwise.

• thisArg (any) – A value to use as this when executing predicate.

Returns:

number – The index of the first element in the Sequence that satisfies the provided testing function.

PySequence.forEach(callbackfn, thisArg)

See Array.forEach(). Executes a provided function once for each Sequence element.

Arguments:

• callbackfn ((elt: any) => void) – A function to execute for each element in the Sequence. Its return value is discarded.

• thisArg (any) – A value to use as this when executing callbackFn.

PySequence.includes(elt)

The Array.includes() method determines whether a Sequence includes a certain value among its entries, returning true or false as appropriate.

Arguments:

• elt (any)

Returns:

any

PySequence.indexOf(elt, fromIndex)

See Array.indexOf(). Returns the first index at which a given element can be found in the Sequence, or -1 if it is not present.

Arguments:

• elt (any) – Element to locate in the Sequence.

• fromIndex (number) – Zero-based index at which to start searching, converted to an integer. Negative index counts back from the end of the Sequence.

Returns:

number – The first index of the element in the Sequence; -1 if not found.

PySequence.join(separator)

See Array.join(). The Array.join() method creates and returns a new string by concatenating all of the elements in the Sequence.

Arguments:

• separator (string) – A string to separate each pair of adjacent elements of the Sequence.

Returns:

string – A string with all Sequence elements joined.

PySequence.keys()

The Array.keys() method returns a new iterator object that contains the keys for each index in the Sequence.

Returns:

IterableIterator<number> – A new iterator object.

PySequence.lastIndexOf(elt, fromIndex)

See Array.lastIndexOf(). Returns the last index at which a given element can be found in the Sequence, or -1 if it is not present.

Arguments:

• elt (any) – Element to locate in the Sequence.

• fromIndex (number) – Zero-based index at which to start searching backwards, converted to an integer. Negative index counts back from the end of the Sequence.

Returns:

number – The last index of the element in the Sequence; -1 if not found.

PySequence.map<U>(callbackfn, thisArg)

See Array.map(). Creates a new array populated with the results of calling a provided function on every element in the calling Sequence.

Type parameters:

U –

Arguments:

• callbackfn ((elt: any, index: number, array: any) => U) – A function to execute for each element in the Sequence. Its return value is added as a single element in the new array.

• thisArg (any) – A value to use as this when executing callbackFn.

Returns:

U[]

PySequence.reduce(callbackfn, initialValue)

See Array.reduce(). Executes a user-supplied “reducer” callback function on each element of the Sequence, in order, passing in the return value from the calculation on the preceding element. The final result of running the reducer across all elements of the Sequence is a single value.

Arguments:

• callbackfn ((previousValue: any, currentValue: any, currentIndex: number, array: any) => any) – A function to execute for each element in the Sequence. Its return value is discarded.

• initialValue (any)

Returns:

any

PySequence.reduceRight(callbackfn, initialValue)

See Array.reduceRight(). Applies a function against an accumulator and each value of the Sequence (from right to left) to reduce it to a single value.

Arguments:

• callbackfn ((previousValue: any, currentValue: any, currentIndex: number, array: any) => any) – A function to execute for each element in the Sequence. Its return value is discarded.

• initialValue (any)

Returns:

any

PySequence.slice(start, stop)

See Array.slice(). The Array.slice() method returns a shallow copy of a portion of a Sequence into a new array object selected from start to stop (stop not included)

Arguments:

• start (number) – Zero-based index at which to start extraction. Negative index counts back from the end of the Sequence.

• stop (number) – Zero-based index at which to end extraction. Negative index counts back from the end of the Sequence.

Returns:

any – A new array containing the extracted elements.

PySequence.some(predicate, thisArg)

See Array.some(). Tests whether at least one element in the Sequence passes the test implemented by the provided function.

Arguments:

• predicate ((value: any, index: number, array: any[]) => unknown) – A function to execute for each element in the Sequence. It should return a truthy value to indicate the element passes the test, and a falsy value otherwise.

• thisArg (any) – A value to use as this when executing predicate.

Returns:

boolean

PySequence.toJSON(this)

Arguments:

• this (any)

Returns:

unknown[]

PySequence.values()

The Array.values() method returns a new iterator object that contains the values for each index in the Sequence.

Returns:

IterableIterator – A new iterator object.

class pyodide.ffi.PythonError()

A JavaScript error caused by a Python exception.

In order to reduce the risk of large memory leaks, the PythonError contains no reference to the Python exception that caused it. You can find the actual Python exception that caused this error as sys.last_exc.

See type translations of errors for more information.

Avoid leaking stack Frames

If you make a PyProxy of sys.last_exc, you should be especially careful to destroy() it when you are done. You may leak a large amount of memory including the local variables of all the stack frames in the traceback if you don’t. The easiest way is to only handle the exception in Python.

Extends:

• Error

PythonError.type

type: string

The name of the Python error class, e.g, RuntimeError or KeyError.

pyodide.canvas

This provides APIs to set a canvas for rendering graphics.

For example, you need to set a canvas if you want to use the SDL library. See Using SDL-based packages in Pyodide for more information.

Functions:

getCanvas2D()	Get the HTML5 canvas element used for 2D rendering.
getCanvas3D()	Get the HTML5 canvas element used for 3D rendering.
setCanvas2D(canvas)	Set the HTML5 canvas element to use for 2D rendering.
setCanvas3D(canvas)	Set the HTML5 canvas element to use for 3D rendering.

pyodide.canvas.getCanvas2D()

Get the HTML5 canvas element used for 2D rendering. For now, Emscripten only supports one canvas element, so getCanvas2D and getCanvas3D are the same.

Returns:

HTMLCanvasElement | undefined

pyodide.canvas.getCanvas3D()

Get the HTML5 canvas element used for 3D rendering. For now, Emscripten only supports one canvas element, so getCanvas2D and getCanvas3D are the same.

Returns:

HTMLCanvasElement | undefined

pyodide.canvas.setCanvas2D(canvas)

Set the HTML5 canvas element to use for 2D rendering. For now, Emscripten only supports one canvas element, so setCanvas2D and setCanvas3D are the same.

Arguments:

• canvas (HTMLCanvasElement)

pyodide.canvas.setCanvas3D(canvas)

Set the HTML5 canvas element to use for 3D rendering. For now, Emscripten only supports one canvas element, so setCanvas2D and setCanvas3D are the same.

Arguments:

• canvas (HTMLCanvasElement)