webbrowser.open with file: URLs may launch editor instead of browser

Bug report

Transferred to https://discuss.python.org/t/support-for-file-urls-in-webbrowser-open/81612 until consensus is reached.

Bug description:

In the code:

import webbrowser
from pathlib import Path

index_html = Path.cwd() / "index.html"
webbrowser.open(index_html.as_uri())

It is common for xdg-open (on linux) or open location (on mac) or os.startfile (on windows) to be selected as the default browser. This is great and simple for http[s] urls, but when these are passed file:// urls, all of the above select the default opener for HTML files, which may not be a browser at all (commonly a text editor for developer systems).

I don't know if there's a way to indicate that Browser entries can handle given URL schemes, but when selecting a browser from the try list, ideally these generic 'open' mechanisms should be skipped for file: URLs. Even better, use standard APIs to lookup the default browsers for http[s] and invoke that explicitly, rather than relying on an interpretation of "open URL" which is only valid for http URLs.

I believe URLForApplicationToOpenURL is the current macOS API to look up the application for http:, which could be used to launch explicitly with a browser. I guess xdg-settings get is already the equivalent for most linux situations and preferred if available, which is great. I'm not sure there's a more general way to discover what xdg-open will do with http://, but we have occasional reports where xdg-settings get default-web-browser doesn't work and xdg-open is invoked and doesn't launch a browser (or launches a different browser). I've no idea what the Windows call would be, but this looks like the same question.

This appears to have been opened long ago as #37540 and erroneously closed as an Apple bug (all platforms exhibit this behavior, and I think the bug is pretty clearly in webbrowser's assumption that "open file://path.html" means "open file://path.html with a web browser" which does not appear to be what any of the platforms mean by the chosen API).

CPython versions tested on:

3.9, 3.10, 3.11, 3.12

Operating systems tested on:

Linux, macOS, Windows

Linked PRs

• gh-130031
• gh-130535
• gh-130538
• gh-130541

Read Lib/webbrowser.py at the Linux xdg-open, Windows os.startfile, and macOS open location implementations linked in the report. Review the transferred discussion and linked PRs first, since consensus and proposed work are elsewhere. Done would require an agreed cross-platform behavior for file: URLs and corresponding tests.