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gh-149720: Remove support for undotted ext in mimetypes.MimeType.add_type #149721

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Merged
sobolevn merged 3 commits into from
May 12, 2026
Merged

gh-149720: Remove support for undotted ext in mimetypes.MimeType.add_type #149721

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9c8bc62
gh-149720: Remove support for undotted `ext` in `mimetypes.MimeType.a…
sobolevn May 12, 2026
0a16e9c
Fix typo
sobolevn May 12, 2026
c3dbd0d
Address review
sobolevn May 12, 2026
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8 changes: 8 additions & 0 deletions Doc/library/mimetypes.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -129,10 +129,18 @@ behavior of the module.
Add a mapping from the MIME type *type* to the extension *ext*. When the
extension is already known, the new type will replace the old one. When the type
is already known the extension will be added to the list of known extensions.
Valid extensions are empty or start with a ``'.'``.

When *strict* is ``True`` (the default), the mapping will be added to the
official MIME types, otherwise to the non-standard ones.

.. deprecated:: 3.14
*ext* values that do not start with ``'.'`` are deprecated.

.. versionchanged:: next
*ext* now must start with ``'.'``. Otherwise :exc:`ValueError` is raised.



.. data:: inited

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7 changes: 7 additions & 0 deletions Doc/whatsnew/3.16.rst
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Expand Up @@ -127,6 +127,13 @@ logging
and scheduled for removal in Python 3.16. Define handlers with the *stream*
argument instead.

mimetypes
---------

* Valid extensions start with a '.' or are empty for
:meth:`mimetypes.MimeTypes.add_type`.
Undotted extensions now raise a :exc:`ValueError`.

symtable
--------

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9 changes: 1 addition & 8 deletions Lib/mimetypes.py
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Expand Up @@ -93,14 +93,7 @@ def add_type(self, type, ext, strict=True):
Valid extensions are empty or start with a '.'.
"""
if ext and not ext.startswith('.'):
from warnings import _deprecated

_deprecated(
"Undotted extensions",
"Using undotted extensions is deprecated and "
"will raise a ValueError in Python {remove}",
remove=(3, 16),
)
raise ValueError(f"Extension {ext!r} must start with '.'")

if not type:
return
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7 changes: 5 additions & 2 deletions Lib/test/test_mimetypes.py
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Expand Up @@ -389,9 +389,12 @@ def test_added_types_are_used(self):
mime_type, _ = mimetypes.guess_type('test.myext')
self.assertEqual(mime_type, 'testing/type')

def test_add_type_with_undotted_extension_deprecated(self):
with self.assertWarns(DeprecationWarning):
def test_add_type_with_undotted_extension_not_supported(self):
msg = "Extension 'undotted' must start with '.'"
with self.assertRaisesRegex(ValueError, msg):
mimetypes.add_type("testing/type", "undotted")
with self.assertRaisesRegex(ValueError, msg):
mimetypes.add_type("", "undotted")


@unittest.skipUnless(sys.platform.startswith("win"), "Windows only")
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2026-05-12-14-44-39.gh-issue-149720.ccsoW-.rst
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@@ -0,0 +1 @@
Remove support for undotted *ext* in :meth:`mimetypes.MimeTypes.add_type`.
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