(loading_packages)= # Loading packages Only the Python standard library and six are available after importing Pyodide. To use other libraries, you’ll need to load their package using either, - {ref}`pyodide.loadPackage ` for packages built with pyodide. - `micropip.install` for pure Python packages with wheels available on PyPi or on other URLs. ```{note} Note that `micropip` can also be used to load packages built in pyodide (in which case it relies on {ref}`pyodide.loadPackage `). ``` Alternatively you can run Python code without manually pre-loading packages. You can do this with {ref}`pyodide.runPythonAsync `) function, which will automatically download all packages that the code snippet imports. It only supports packages included in Pyodide (not on PyPi) at present. ## Loading packages with pyodide.loadPackage Packages can be loaded by name, for those included in the official pyodide repository using, ```js pyodide.loadPackage('numpy') ``` It is also possible to load packages from custom URLs, ```js pyodide.loadPackage('https://foo/bar/numpy.js') ``` in which case the URL must end with `.js`. When you request a package from the official repository, all of that package's dependencies are also loaded. Dependency resolution is not yet implemented when loading packages from custom URLs. Multiple packages can also be loaded in a single call, ```js pyodide.loadPackage(['cycler', 'pytz']) ``` `pyodide.loadPackage` returns a `Promise`. ```javascript pyodide.loadPackage('matplotlib').then(() => { // matplotlib is now available }); ``` (micropip)= ## Micropip ### Installing packages from PyPI Pyodide supports installing pure Python wheels from PyPI with `micropip`. You can use the `then` method on the `Promise` that {func}`micropip.install` returns to do work once the packages have finished loading: ```py def do_work(*args): import snowballstemmer stemmer = snowballstemmer.stemmer('english') print(stemmer.stemWords('go goes going gone'.split())) import micropip micropip.install('snowballstemmer').then(do_work) ``` Micropip implements file integrity validation by checking the hash of the downloaded wheel against pre-recorded hash digests from the PyPi JSON API. (micropip-installing-from-arbitrary-urls)= ### Installing wheels from arbitrary URLs Pure python wheels can also be installed from any URL with micropip, ```py import micropip micropip.install( 'https://example.com/files/snowballstemmer-2.0.0-py2.py3-none-any.whl' ) ``` The wheel name in the URL must follow [PEP 427 naming convention](https://www.python.org/dev/peps/pep-0427/#file-format), which will be the case if the wheels is made using standard python tools (`pip wheel`, `setup.py bdist_wheel`). All required dependencies need also to be previously installed with `micropip` or `pyodide.loadPackage`. The remote server must set Cross-Origin Resource Sharing (CORS) headers to allow access. Otherwise, you can prepend a CORS proxy to the URL. Note however that using third-party CORS proxies has security implications, particularly since we are not able to check the file integrity, unlike with installs from PyPi. ## Example Adapting the setup from the section on {ref}`using_from_javascript` a complete example would be, ```html ```