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When trying to load a Python script from a separate file using PyScript, I get the following error:

JsException(TypeError: Failed to fetch)

How can I fix this error and run the Python script?

My source code consists of two files, hello.html and hello.py.

hello.html:

<html>
  <head>
    <title>Hello PyScript</title>
    <meta charset="utf-8" />
    <link rel="stylesheet" href="https://pyscript.net/alpha/pyscript.css" />
    <script defer src="https://pyscript.net/alpha/pyscript.js"></script>
  </head>
  <py-env>
- paths:
  - /hello.py
  </py-env>
  <body>
    <py-script src="./hello.py"></py-script>
  </body>
</html>

hello.py:

print("Hello, PyScript!")

In the developer tools, the console displays the following error:

Access to fetch at 'file:///hello.py' from origin 'null' has been blocked by CORS policy: Cross origin requests are only supported for protocol schemes: http, data, chrome, chrome-extension, chrome-untrusted, https.

I am opening the file by double-clicking on it in file explorer.

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6
  • It is not a Pyscript issue. It is a because a are running the file directly. You need a webserver like nginx, httpd or any othe for development stage Commented May 7, 2022 at 11:40
  • 1
    No, it's not a PyScript issue, at least not directly. But it does look like a PyScript issue to beginners, so I wrote this question and answer so that people would find this page when searching about their problem. Commented May 9, 2022 at 4:44
  • 1
    Indeed, it may be the first error that a Pyscript beginner may face ! Commented May 9, 2022 at 12:54
  • 1
    @RichVel: Did you also have a CORS Issue? I got this introduced since today, already made an issue on Github. http.server did not solve it for me Commented May 13, 2022 at 17:43
  • 1
    The code above does need a local HTTP server for both the HTML file and hello.py to fix this CORS issue. The similar looking issue that @DataMastery and I had with download of pyscript.js was actually unrelated to this - it was fixed by the PyScript project on 13th May, the same day it was reported. Commented May 14, 2022 at 18:06

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This error occurs because you are trying to load the file locally, using the file protocol scheme. (In other words, the URL of the page looks something like file:///path/to/hello.html.) When using the file protocol scheme, all major browsers disallow loading other files in the same folder for security reasons. Instead, you need to set up a local server to host your files.

For example, you can set up a test server with Python by running the following command in the folder your files are in:

python -m http.server

(This assumes you have Python 3 installed, and the python command points to your Python 3 installation.)

Once you have started your local server with this command, you will be able to access hello.html at the URL http://localhost:8000/hello.html. When you access it this way, your browser will see that hello.html and hello.py both come from the same origin, so it will allow you to load hello.py from hello.html.

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2 Comments

but also i get the same error when i use:- <py-env> - math </py-env>
@aymhenry The math module is in the standard library, so you should be able to use import math in a py-script tag without using a py-env tag.

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