gh-132054: Add application/yaml to mimetypes

Doc/whatsnew/3.14.rst

@@ -829,6 +829,10 @@ mimetypes
 
   (Contributed by Hugo van Kemenade in :gh:`129965`.)
 
+* Add :rfc:`9512` ``application/yaml`` MIME type for YAML files (``.yaml``
+  and ``.yml``). (Contributed by Sasha "Nelie" Chernykh and Hugo van Kemenade
+  in :gh:`132056`.)
+
 
 multiprocessing
 ---------------

Lib/mimetypes.py

@@ -544,6 +544,8 @@ def _default_mime_types():
         '.rdf'    : 'application/xml',
         '.wsdl'   : 'application/xml',
         '.xpdl'   : 'application/xml',
+        '.yaml'   : 'application/yaml',
+        '.yml'    : 'application/yaml',
         '.zip'    : 'application/zip',
         '.3gp'    : 'audio/3gpp',
         '.3gpp'   : 'audio/3gpp',

Lib/test/test_mimetypes.py

@@ -244,6 +244,7 @@ def check_extensions():
                 ("application/x-texinfo", ".texi"),
                 ("application/x-troff", ".roff"),
                 ("application/xml", ".xsl"),
+                ("application/yaml", ".yaml"),
                 ("audio/flac", ".flac"),
                 ("audio/matroska", ".mka"),
                 ("audio/mp4", ".m4a"),
@@ -286,6 +287,26 @@ def check_extensions():
         mimetypes.init()
         check_extensions()
 
+    def test_guess_file_type(self):
+        def check_file_type():
+            for mime_type, ext in (
+                ("application/yaml", ".yaml"),
+                ("application/yaml", ".yml"),
+                ("audio/mpeg", ".mp2"),
+                ("audio/mpeg", ".mp3"),
+                ("video/mpeg", ".m1v"),
+                ("video/mpeg", ".mpe"),
+                ("video/mpeg", ".mpeg"),
+                ("video/mpeg", ".mpg"),
+            ):
+                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()
+
     def test_init_stability(self):
         mimetypes.init()
 

Misc/NEWS.d/next/Library/2025-04-03-20-28-54.gh-issue-132054.c1nlOx.rst

@@ -0,0 +1,2 @@
+The ``application/yaml`` mime type (:rfc:`9512`) is now supported
+by :mod:`mimetypes`. Patch by Sasha "Nelie" Chernykh and Hugo van Kemenade.