Hey Christian,
There are no docs, and it isn't using x-callback-url. I didn't know about that spec when I did Scan Code. Maybe for a future update...
You have the right URL to launch Scan Code.
scancode://scan?callback=myapp://some.callback/url/path
Scan Code will open the callback url while appending a `code` param
myapp://some.callback/url/path?code=urlEncodedQrCodeData
Your app can then parse the query string for the `code` param. I don't know how flexible Pythonista is, but you would need to hook into the AppDelegate's `application:openURL:sourceApplication:annotation`.
Let me know how it works out for you!