Pyscript ftplib Cors issues in py-env

Hello Guys,
I’m running into an issue where ftplib can’t be used as a library inside of the py-env in the browser. It’s being blocked by cors.

“Access to fetch at ‘’ from origin ‘’ has been blocked by CORS policy: No ‘Access-Control-Allow-Origin’ header is present on the requested resource. If an opaque response serves your needs, set the request’s mode to ‘no-cors’ to fetch the resource with CORS disabled.”

You can go to and see that the pyscript runs well when ftplib is not specified to be used in the browser. However when i’m trying to use ftplib to grab files from a server it hits me with a cors error. It isn’t because of my own server. The reason why I know it isn’t. Is because i’m using jupyter’s notebook on my computer to access the same server over ftplib and I get no errors.

Hi @coreytmayweather, and welcome to the forum! Interesting issue there - a couple of things to help us understand the issue better:

  • Can you copy and paste your python and HTML files inside of a codeblock in this thread? That’s text ```surrounded by three backticks like this```, which makes it show up as a block of code, which we can copy/paste and try for ourselves instead of retyping the screenshots
  • It looks like that firebase app hasn’t been published yet; this is what I see when I follow that link:

Here’s the github of everything.

Hey Guys,
You can load it up on vscode if you have live preview. The code in question is in the home.html. in the first “py-env”. If you go live with the server. and go to the console you can see that the ftplib will cause a cors issue.

Thank you for your help!

Hello Jeff,
Apologies the website link is, and it’s updated in the original post.

Thank you for your reply!