pyodide/docs/loading_packages.md

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(loading_packages)=
# Loading packages
Only the Python standard library and six are available after importing Pyodide.
To use other libraries, youll need to load their package using either,
- {ref}`pyodide.loadPackage <js_api_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
<js_api_pyodide_loadPackage>`).
```
Alternatively you can run Python code without manually pre-loading packages.
You can do this with {ref}`pyodide.runPythonAsync
<api_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 `<package-name>.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.
For use in Iodide:
```
%% py
import micropip
micropip.install('snowballstemmer')
# Iodide implicitly waits for the promise to resolve when the packages have finished
# installing...
%% py
import snowballstemmer
stemmer = snowballstemmer.stemmer('english')
stemmer.stemWords('go goes going gone'.split())
```
For use outside of Iodide (just Python), you can use the `then` method on the
`Promise` that {func}`micropip.install` returns to do work once the packages have
finished loading:
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```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)
```
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Micropip implements file integrity validation by checking the hash of the
downloaded wheel against pre-recorded hash digests from the PyPi JSON API.
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(micropip-installing-from-arbitrary-urls)=
### Installing wheels from arbitrary URLs
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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
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be the case if the wheels is made using standard python tools (`pip wheel`,
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`setup.py bdist_wheel`).
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All required dependencies need also to be previously installed with `micropip`
or `pyodide.loadPackage`.
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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
<html>
<head>
<meta charset="utf-8">
</head>
<body>
<script type="text/javascript">
// set the pyodide files URL (packages.json, pyodide.asm.data etc)
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window.languagePluginUrl = 'https://cdn.jsdelivr.net/pyodide/v0.16.1/full/';
</script>
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<script type="text/javascript" src="https://cdn.jsdelivr.net/pyodide/v0.16.1/full/pyodide.js"></script>
<script type="text/javascript">
pythonCode = `
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)
`
languagePluginLoader.then(() => {
return pyodide.loadPackage(['micropip'])
}).then(() => {
pyodide.runPython(pythonCode);
})
</script>
</body>
</html>
```