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.

Installation

First, go to https://pyscript.net and download the PyScript assets. Unzip the archive to a directory where you wish to write PyScript-enabled HTML files. You should then have three files in your directory.

├── ./
│   ├── pyscript.css
│   ├── pyscript.js
│   └── pyscript.js.map

Your first PyScript HTML file

Here's a "Hello, world!" example using PyScript using the assets you downloaded from https://pyscript.net.

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="pyscript.css" />
    <script defer src="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 8 tags provided by PyScript.

The py-script tag

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

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

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

Writing into labeled elements

In the example above we had a single <py-script> tag and it printed 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 write to.

<html>
    <head>
      <link rel="stylesheet" href="pyscript.css" />
      <script defer src="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 wallis(n):
    pi = 2
    for i in range(1,n):
        pi *= 4 * i ** 2 / (4 * i ** 2 - 1)
    return pi

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

Packages and modules

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 delcare the dependencies using the <py-env> in the HTML head.

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="pyscript.css" />
      <script defer src="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>

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