gh-132054: Add application/yaml to mimetypes

[Kristinita]

• Issue: Add application/yaml to mimetypes #132054

[cpython-cla-bot]

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[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.