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First steps

It's simple:

  • tell your browser to use PyScript, then,
  • tell PyScript how to run your Python code.

That's it!

For the browser to use PyScript, simply add a <script> tag, whose src attribute references a CDN url for pyscript.core, to your HTML document's <head>. We encourage you to add a reference to optional PyScript related CSS:

Reference PyScript in your HTML
<!doctype html>
        <!-- Recommended meta tags -->
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width,initial-scale=1.0">
        <!-- PyScript CSS -->
        <link rel="stylesheet" href="">
        <!-- This script tag bootstraps PyScript -->
        <script type="module" src=""></script>
        <!-- your code goes here... -->

There are two ways to tell PyScript how to find your code.

  • With a standard HTML <script> tag whose type attribute is either py (for Pyodide) or mpy (for MicroPython). This is the recommended way.
  • Via the bespoke <py-script> (Pyodide) and <mpy-script> (MicroPython) tags. Historically, <py-script> used to be the only way to reference your code.

These should be inserted into the <body> of your HTML document.

In both cases either use the src attribute to reference a Python file containing your code, or inline your code between the opening and closing tags. We recommend you use the src attribute method, but retain the ability to include code between tags for convenience.

Here's a <script> tag with a src attribute containing a URL pointing to a Python file.

A <script> tag with a source file
<script type="mpy" src=""></script>

...and here's a <py-script> tag with inline Python code.

A <py-script> tag with inline code
import sys
from pyscript import display


The <script> and <py-script> / <mpy-script> tags may have the following attributes:

  • src - the content of the tag is ignored and the Python code in the referenced file is evaluated instead. This is the recommended way to reference your Python code.
  • config - your code will only be evaluated after the referenced configuration has been parsed. Since configuration can be JSON or a TOML file, config='{"packages":["numpy"]}' and config="./config.json" or config="./config.toml" are all valid.
  • async - your Python code can contain a top level await.
  • worker - a flag to indicate your Python code is to be run on a web worker instead of the "main thread" that looks after the user interface.
  • target - The id or selector of the element where calls to display() should write their values.
  • terminal - A traditional terminal is shown on the page. As with conventional Python, print statements output here. If the worker flag is set the terminal becomes interactive (e.g. use the input statement to gather characters typed into the terminal by the user).


The packages setting used in the example configuration shown above is for Pyodide using PyPI.

When using MicroPython, and because MicroPython doesn't support code packaged on PyPI, you should use a valid URL to a MicroPython friendly package.

For more information please refer to the packages section of this user guide.


Why do we recommend use of the <script> tag with a src attribute?

Within the HTML standard, the <script> tag is used to embed executable code. Its use case completely aligns with our own, as does its default behaviour.

By referencing a separate Python source file via the src attribute, your code is just a regular Python file your code editor will understand. Python code embedded within a <script> tag in an HTML file won't benefit from the advantages code editors bring: syntax highlighting, code analysis, language-based contextual awareness and perhaps even an AI co-pilot.

Both the <py-script> and <mpy-script> tags with inline code are web components that are not built into the browser. While they are convenient, there is a performance cost to their use.


The browser's tab displaying the website running PyScript is an isolated computing sandbox. Define the Python environment in which your code will run with configuration options (discussed later in this document).


If you want to run code on both the main thread and in a worker, be explicit and use separate tags.

<script type="mpy" src=""></script>  <!-- on the main thread -->
<script type="py" src="" worker config="pyconfig.toml"></script> <!-- on the worker -->

Notice how different interpreters can be used with different configurations.