Getting started with PyScript

This page will guide you through getting started with PyScript.

Development setup

PyScript does not require any development environment other than a web browser. We recommend using Chrome.

If you're using VSCode, the Live Server extension can be used to reload the page as you edit the HTML file.

Installation

There is no installation required. In this document, we'll use the PyScript assets served on https://pyscript.net.

If you want to download the source and build it yourself, follow the instructions in the README.md file.

Your first PyScript HTML file

Here's a "Hello, world!" example using PyScript.

Using your favorite editor, create a new file called hello.html in the same directory as your PyScript, JavaScript, and CSS files with the following content, and open the file in your web browser. You can typically open an HTML by double-clicking it in your file explorer.

<html>
  <head>
    <link rel="stylesheet" href="https://pyscript.net/alpha/pyscript.css" />
    <script defer src="https://pyscript.net/alpha/pyscript.js"></script>
  </head>
  <body> <py-script> print('Hello, World!') </py-script> </body>
</html>

Notice the use of the <py-script> tag in the HTML body. This is where you'll write your Python code. In the following sections, we'll introduce the eight tags provided by PyScript.

The py-script tag

The <py-script> tag lets you execute multi-line Python scripts and print back onto the page. For example, we can compute π.

<html>
  <head>
    <link rel="stylesheet" href="https://pyscript.net/alpha/pyscript.css" />
    <script defer src="https://pyscript.net/alpha/pyscript.js"></script>
  </head>
  <body>
      <py-script>
print("Let's compute π:")
def compute_pi(n):
    pi = 2
    for i in range(1,n):
        pi *= 4 * i ** 2 / (4 * i ** 2 - 1)
    return pi

pi = compute_pi(100000)
s = f"π is approximately {pi:.3f}"
print(s)
      </py-script>
  </body>
</html>

Writing into labeled elements

In the example above, we had a single <py-script> tag printing one or more lines onto the page in order. Within the <py-script>, you have access to the pyscript module, which provides a .write() method to send strings into labeled elements on the page.

For example, we'll add some style elements and provide place holders for the <py-script> tag to write to.

<html>
    <head>
      <link rel="stylesheet" href="https://pyscript.net/alpha/pyscript.css" />
      <script defer src="https://pyscript.net/alpha/pyscript.js"></script>
      <link href="https://cdn.jsdelivr.net/npm/bootstrap@5.1.3/dist/css/bootstrap.min.css" rel="stylesheet" crossorigin="anonymous">
    </head>

  <body>
    <b><p>Today is <u><label id='today'></label></u></p></b>
    <br>
    <div id="pi" class="alert alert-primary"></div>
    <py-script>
import datetime as dt
pyscript.write('today', dt.date.today().strftime('%A %B %d, %Y'))

def compute_pi(n):
    pi = 2
    for i in range(1,n):
        pi *= 4 * i ** 2 / (4 * i ** 2 - 1)
    return pi

pi = compute_pi(100000)
pyscript.write('pi', f'π is approximately {pi:.3f}')
    </py-script>
  </body>
</html>

The py-env tag

In addition to the Python Standard Library and the pyscript module, many 3rd-party OSS packages will work out-of-the-box with PyScript.

In order to use them, you will need to declare the dependencies using the <py-env> tag in the HTML head. You can also link to .whl files directly on disk like in our toga example.

<py-env>
- './static/wheels/travertino-0.1.3-py3-none-any.whl'
</py-env>

If your .whl is not a pure Python wheel, then open a PR or issue with pyodide to get it added here. If there's enough popular demand, the pyodide team will likely work on supporting your package. Regardless, things will likely move faster if you make the PR and consult with the team to get unblocked.

For example, NumPy and Matplotlib are available. Notice here we're using <py-script output="plot"> as a shortcut, which takes the expression on the last line of the script and runs pyscript.write('plot', fig).

<html>
    <head>
      <link rel="stylesheet" href="https://pyscript.net/alpha/pyscript.css" />
      <script defer src="https://pyscript.net/alpha/pyscript.js"></script>
      <py-env>
        - numpy
        - matplotlib
      </py-env>
    </head>

  <body>
    <h1>Let's plot random numbers</h1>
    <div id="plot"></div>
    <py-script output="plot">
import matplotlib.pyplot as plt
import numpy as np

x = np.random.randn(1000)
y = np.random.randn(1000)

fig, ax = plt.subplots()
ax.scatter(x, y)
fig
    </py-script>
  </body>
</html>

Local modules

In addition to packages, you can declare local Python modules that will be imported in the <py-script> tag. For example, we can place the random number generation steps in a function in the file data.py.

# data.py
import numpy as np


def make_x_and_y(n):
    x = np.random.randn(n)
    y = np.random.randn(n)
    return x, y

In the HTML tag <py-env>, paths to local modules are provided in the paths: key.

<html>
    <head>
      <link rel="stylesheet" href="https://pyscript.net/alpha/pyscript.css" />
      <script defer src="https://pyscript.net/alpha/pyscript.js"></script>
      <py-env>
        - numpy
        - matplotlib
        - paths:
          - /data.py
      </py-env>
    </head>

  <body>
    <h1>Let's plot random numbers</h1>
    <div id="plot"></div>
    <py-script output="plot">
import matplotlib.pyplot as plt
from data import make_x_and_y

x, y = make_x_and_y(n=1000)

fig, ax = plt.subplots()
ax.scatter(x, y)
fig
    </py-script>
  </body>
</html>

The py-repl tag

The <py-repl> tag creates a REPL component that is rendered to the page as a code editor, allowing you to write executable code inline.

The py-config tag

Use the <py-config> tag to set and configure general metadata about your PyScript application in YAML format. If you are unfamiliar with YAML, consider reading Red Hat's YAML for beginners guide for more information.

The <py-config> tag can be used as follows:

<py-config>
  - autoclose_loader: false
  - runtimes:
    -
      src: "https://cdn.jsdelivr.net/pyodide/v0.20.0/full/pyodide.js"
      name: pyodide-0.20
      lang: python
</py-config>

The following optional values are supported by <py-config>:

autoclose_loader (boolean): If false, PyScript will not close the loading splash screen when the startup operations finish.
name (string): Name of the user application. This field can be any string and is to be used by the application author for their own customization purposes.
version (string): Version of the user application. This field can be any string and is to be used by the application author for their own customization purposes. It is not related to the PyScript version.
runtimes (List of Runtimes): List of runtime configurations. Each Runtime expects the following fields:
- src (string, Required): URL to the runtime source.
- name (string): Name of the runtime. This field can be any string and is to be used by the application author for their own customization purposes.
- name (string): Programming language supported by the runtime. This field can by used by the application author to provide clarify. It currently has no implications on how PyScript behaves.

Visual component tags

The following tags can be used to add visual attributes to your HTML page.

Tag	Description
`<py-inputbox>`	Adds an input box that can be used to prompt users to enter input values.
`<py-box>`	Creates a container object that can be used to host one or more visual components that define how elements of `<py-box>` should align and show on the page.
`<py-button>`	Adds a button to which authors can add labels and event handlers for actions on the button, such as `on_focus` or `on_click`.
`<py-title>`	Adds a static text title component that styles the text inside the tag as a page title.

All the elements above are experimental and not implemented at their full functionality. Use them with the understanding that the APIs or full support might change or be removed until the visual components are more mature.