gh-132054: Add application/yaml to mimetypes

[Kristinita]

• Issue: Add application/yaml to mimetypes #132054

[brianschubert]

@Kristinita I think you accidentally included some unrelated changes in your last push

[Kristinita]

Type: Reply 💬

@brianschubert, I’m sorry, I made a mistake in the test file and create the new commit that fix tests. I can’t push my changes to GitHub, so I run git fetch, git rebase and then push changes to GitHub.

I can close this pull request, update my CPython fork and send a new pull request. Or should I do something else? I can’t find instructions for this case in Python Developer’s Guide.

I apologize for the concern.

Thanks.

[brianschubert]

No worries! And no need to open a new PR. You can undo the extra changes by running git restore -s HEAD~1 ./ (which will reset your working tree to what it was before the commit), then remake the intended change to test_mimetypes.py and create a new commit.

[AA-Turner]

@Kristinita please read our AI policy.

A

[Kristinita]

Type: Fixed ✔️

@brianschubert , done. All checks have passed now.

Thanks.

[hugovk]

Please could you add it to What's New?

https://docs.python.org/3.14/whatsnew/3.14.html#mimetypes

And add a test for .yml?

[Kristinita]

Type: Question ❓

1. Question

And add a test for .yml?

@hugovk, what is the preferred format for tests for non-preferred extensions like .yml? I was looking for the answer to this in previous pull requests that add new media types, but I can’t find a conventional method.

2. Missing tests

Currently, the file test_mimetypes.py in many cases contains tests solely for preferred extensions. Examples:

1. For audio/mpeg media type: test_mimetypes.py has the test for the .mp3 preferred extension, but not for the non-preferred extension .mp2.
2. For video/mpeg media type: test_mimetypes.py has the test for the .mpeg preferred extension, but not for non-preferred extensions .m1v, .mpa, .mpe and .mpg.

3. Existing test for non-preferred extensions

Should I create a test like the test for the text/plain media type?

cpython/Lib/test/test_mimetypes.py

Lines 177 to 179 in ef17252

	all = self.db.guess_all_extensions('text/plain', strict=True)
	self.assertTrue(set(all) >= {'.bat', '.c', '.h', '.ksh', '.pl', '.txt'})
	self.assertEqual(len(set(all)), len(all)) # no duplicates

4. Simpler adding tests

Possibly, it would be nice if adding tests for non-preferred extension will be simpler. For example, the file test_mimetypes.py could have a function like test_non_preferred_extensions to which users will be able to add all non-preferred extensions for media types. Example:

("application/yaml", ".yml"),
("audio/mpeg", ".mp2"),
("video/mpeg", ".m1v"),
("video/mpeg", ".mpa"),
("video/mpeg", ".mpe"),
("video/mpeg", ".mpg")

Thanks.

[hugovk]

We could add some a test case to check the output of guess_file_type is as expected, for example:

    def test_guess_file_type(self):
        def check_file_type():
            for mime_type, ext in (
                ("application/yaml", ".yaml"),
                ("application/yaml", ".yml"),
            ):
                with self.subTest(mime_type=mime_type, ext=ext):
                    result, _ = mimetypes.guess_file_type(f"filename{ext}")
                    self.assertEqual(result, mime_type)

        check_file_type()
        mimetypes.init()
        check_file_type()

No need to exhaustively fill lots of other preferred+optional extensions, but we could include a few more, such as the audio/mpeg and video/mpeg ones mentioned.

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[hugovk]

Updated to add tests and a What's New entry.

The What's New for mimetypes is getting a bit sprawling, but we can copyedit that later as part of #123299.

@Kristinita Thank you and congratulations on your first contribution to CPython!

[hugovk]

@Kristinita We can put your full name here if you like.

[Kristinita]

@hugovk, thanks for adding the function test_guess_file_type()!

My contribution here is insignificant, and I think it would be more fair if you will add your name instead of my.

(But if the name of the author of the pull request is required, perhaps, Sasha “Nelie” Chernykh instead of Kristinita would be better).

Thanks.

[hugovk]

You contribution is not insignificant. I've put both our names there, thanks again!