Windows 10 Mimetypes for .webp return empty

[ewwink]

Bug report

Bug description:

on Windows 10 guess_file_type() checking .webp file return tuple('', None) not tuple('image/webp', None)

The problem is db.read_windows_registry() overwrite default types_map .webp = 'image/webp' into .webp = ''

cpython/Lib/mimetypes.py

Lines 390 to 393 in 65da5db

	if files is None or _db is None:
	db = MimeTypes()
	# Quick return if not supported
	db.read_windows_registry()

CPython versions tested on:

3.11, 3.12, 3.13

Operating systems tested on:

Windows

Linked PRs

• gh-128703: Fix mimetypes.guess_type for empty Content-Type in registry #128854
• [3.13] gh-128703: Fix mimetypes.guess_type for empty Content-Type in registry (GH-128854) #130121
• [3.12] gh-128703: Fix mimetypes.guess_type for empty Content-Type in registry (GH-128854) #130122

[zooba]

Can you check the value of HKEY_CLASSES_ROOT\.webp's ContentType value on your machine?

mimetypes intentionally prefers the system database, so if you've installed something that modified your system, then you would expect to see the changes.

FWIW, my own machines specify image/webp in that value.

[ewwink]

it has ContentType and Content Type (with space)

for other extensions it use Content Type (with space)

[zooba]

Right, so something has registered the type incorrectly. There isn't really any easy way to find out who did it, but deleting the empty Content Type entry and renaming the ContentType one should fix your system.

[ewwink]

yes that should fix the problem, but how if the extension has no Content Type value, for example the .ras

or even it has no Content Type

wouldn't it be better to check for empty value, if yes then do not overwrite the original value of types_map = _types_map_default = {...

[ewwink]

Python 3.12 on Ubuntu (fresh install)

# python -V
Python 3.12.8
# cat /usr/lib/python3.12/mimetypes.py | grep webp
        '.webp': 'image/webp',
# python
>>> import mimetypes
>>> mimetypes.guess_type('picture.jpg')
('image/jpeg', None)
>>> mimetypes.guess_type('picture.webp')
(None, None)

update:
3.10: no support for .webp
3.11, 3.12: need strict=False mimetypes.guess_type('picture.webp', strict=False)
3.13: work without additional arg

Quick Fix for Python 3.12 or lower, locate the original path of mimetypes.py and replace with version 3.13

# wget -O /usr/lib/pythonX.XX/mimetypes.py https://raw.githubusercontent.com/python/cpython/refs/heads/3.13/Lib/mimetypes.py

[zooba]

Ignoring empty values is a reasonable idea. PRs welcome from anyone (there's both Python and C versions of this code, IIRC).

[rruuaanng]

I will take a look at it later. If it's allowed, please leave it for me.
(That is, after reading the registry, check whether the read Content Type field is an empty string. I hope I didn't misunderstand)

[ewwink]

I will take a look at it later. If it's allowed, please leave it for me. (That is, after reading the registry, check whether the read Content Type field is an empty string. I hope I didn't misunderstand)

yes that's right, problematic code

cpython/Lib/mimetypes.py

Line 93 in 1153e66

self.types_map[strict][ext] = type

I replace with

        if not type and ext in self.types_map[strict]:
            type = self.types_map[strict][ext]
        self.types_map[strict][ext] = type

do you think it is good idea to also update another version?
3.10: Add support for .webp and other extension like in 3.13 + check empty value
3.11, 3.12: Remove strict=False requirement + check empty value
3.13: only check empty value

[rruuaanng]

only check empty value

I think this is all I need, we should fix the bug first and then make some improvements to it later, but this requires more discussion.