mimetypes.add_type should complain when you give it an undotted ext

@OddBloke

BPO	31040
Nosy	@OddBloke, @JimJJewett, @JulienPalard, @rcj4747
PRs	bpo-31040: Add warning note about mimetypes.add_type ext argument format #2871 gh-75223: Reject undotted extensions in `mimetypes.add_type()` #2895

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-07-25.19:25:41.891>
labels = ['3.7', 'library', 'docs']
title = 'mimetypes.add_type should complain when you give it an undotted ext'
updated_at = <Date 2019-09-13.10:59:42.020>
user = 'https://github.com/OddBloke'

bugs.python.org fields:

activity = <Date 2019-09-13.10:59:42.020>
actor = 'mdk'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation', 'Library (Lib)']
creation = <Date 2017-07-25.19:25:41.891>
creator = 'odd_bloke'
dependencies = []
files = []
hgrepos = []
issue_num = 31040
keywords = []
message_count = 4.0
messages = ['299135', '306501', '352266', '352286']
nosy_count = 5.0
nosy_names = ['odd_bloke', 'docs@python', 'Jim.Jewett', 'mdk', 'rcj']
pr_nums = ['2871', '2895']
priority = 'normal'
resolution = None
stage = 'commit review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue31040'
versions = ['Python 3.7']

Linked PRs

import mimetypes

print(mimetypes.guess_type('foo.manifest'))
mimetypes.add_type('text/plain', 'manifest')
print(mimetypes.guess_type('foo.manifest'))

results in:

('application/x-ms-manifest', None)
('application/x-ms-manifest', None)

I (mistakenly) expected the latter print to give me "('text/plain', None)". It doesn't because I should have prepended a . to the second add_type argument.

I think add_type should error out when given an extension without a dot-prefix, because it's extremely unlikely that code that does so is behaving as intended with the current implementation.

(At the very least, documentation should be updated to make this expectation clearer.)

Ideally, use .startswith('.') Instead if find, but this is a clear UI fix. First pull request fixes doc, second fixes code. OK to apply both.

I think we should deprecate calling add_type with an empty ext, as I don't think it's a feature, more a side effect of the current implementation.

But as some may use it like a feature, I asked the current PR to emit a warning, to not break the current implementations.

To be able to simplify in the future, why not deprecating empty ext so we can remove it in a few versions?

I just found a case where the empty mime type is actually usefull, it's in Lib/http/server.py:

    extensions_map = mimetypes.types_map.copy()
    extensions_map.update({
        '': 'application/octet-stream', # Default
        '.py': 'text/plain',
        '.c': 'text/plain',
        '.h': 'text/plain',
        })

It does *not* uses add_type, but demos the fact that the empty type may be usefull from time to time, maybe don't warn and don't deprecate it at all.

Checking the top 8k PyPI projects:

Details

❯ python3 ~/github/misc/cpython/search_pypi_top.py -q . mimetypes.add_type
./django_pipeline-3.1.0.tar.gz: django_pipeline-3.1.0/pipeline/utils.py: mimetypes.add_type(type, ext)
./dagster-webserver-1.9.0.tar.gz: dagster-webserver-1.9.0/dagster_webserver/webserver.py: mimetypes.add_type("application/javascript", ".js")
./dagster-webserver-1.9.0.tar.gz: dagster-webserver-1.9.0/dagster_webserver/webserver.py: mimetypes.add_type("text/css", ".css")
./dagster-webserver-1.9.0.tar.gz: dagster-webserver-1.9.0/dagster_webserver/webserver.py: mimetypes.add_type("image/svg+xml", ".svg")
./dash-2.18.1.tar.gz: dash-2.18.1/dash/dash.py: mimetypes.add_type("application/json", ".map", True)
./chainlit-1.3.1.tar.gz: chainlit-1.3.1/chainlit/server.py: mimetypes.add_type("application/javascript", ".js")
./chainlit-1.3.1.tar.gz: chainlit-1.3.1/chainlit/server.py: mimetypes.add_type("text/css", ".css")
./ansible-10.5.0.tar.gz: ansible-10.5.0/ansible_collections/azure/azcollection/plugins/modules/azure_rm_storageblob.py: mimetypes.add_type('application/json', '.json')
./ansible-10.5.0.tar.gz: ansible-10.5.0/ansible_collections/azure/azcollection/plugins/modules/azure_rm_storageblob.py: mimetypes.add_type('application/javascript', '.js')
./ansible-10.5.0.tar.gz: ansible-10.5.0/ansible_collections/azure/azcollection/plugins/modules/azure_rm_storageblob.py: mimetypes.add_type('application/wasm', '.wasm')
./django_filer-3.2.3.tar.gz: django_filer-3.2.3/filer/apps.py: mimetypes.add_type("image/heic", ext)
./django_filer-3.2.3.tar.gz: django_filer-3.2.3/filer/apps.py: mimetypes.add_type("image/webp", ".webp")
./EbookLib-0.18.tar.gz: EbookLib-0.18/ebooklib/utils.py: mimetypes.add_type('application/xhtml+xml', '.xhtml')
./fava-1.29.tar.gz: fava-1.29/src/fava/application.py: mimetypes.add_type("text/javascript", ".js")
./ansible-10.5.0.tar.gz: ansible-10.5.0/ansible_collections/community/general/tests/integration/targets/launchd/files/ansible_test_service.py: mimetypes.add_type('application/json', '.json')
./azure_cli-2.65.0.tar.gz: azure_cli-2.65.0/azure/cli/command_modules/storage/util.py: mimetypes.add_type('application/json', '.json')
./azure_cli-2.65.0.tar.gz: azure_cli-2.65.0/azure/cli/command_modules/storage/util.py: mimetypes.add_type('application/javascript', '.js')
./azure_cli-2.65.0.tar.gz: azure_cli-2.65.0/azure/cli/command_modules/storage/util.py: mimetypes.add_type('application/wasm', '.wasm')
./jupyter_server-2.14.2.tar.gz: jupyter_server-2.14.2/jupyter_server/serverapp.py: mimetypes.add_type("text/css", ".css")
./jupyter_server-2.14.2.tar.gz: jupyter_server-2.14.2/jupyter_server/serverapp.py: mimetypes.add_type("application/javascript", ".js")
./jupyter_server-2.14.2.tar.gz: jupyter_server-2.14.2/jupyter_server/serverapp.py: mimetypes.add_type("application/wasm", ".wasm")
./jupyterlab_server-2.27.3.tar.gz: jupyterlab_server-2.27.3/jupyterlab_server/licenses_handler.py: mimetypes.add_type("text/markdown", ".md")
./locust-2.32.1.tar.gz: locust-2.32.1/locust/web.py: mimetypes.add_type("application/javascript", ".js")
./openpyxl-3.1.5.tar.gz: openpyxl-3.1.5/openpyxl/packaging/manifest.py: mimetypes.add_type('application/xml', ".xml")
./openpyxl-3.1.5.tar.gz: openpyxl-3.1.5/openpyxl/packaging/manifest.py: mimetypes.add_type('application/vnd.openxmlformats-package.relationships+xml', ".rels")
./openpyxl-3.1.5.tar.gz: openpyxl-3.1.5/openpyxl/packaging/manifest.py: mimetypes.add_type("application/vnd.ms-office.vbaProject", ".bin")
./openpyxl-3.1.5.tar.gz: openpyxl-3.1.5/openpyxl/packaging/manifest.py: mimetypes.add_type("application/vnd.openxmlformats-officedocument.vmlDrawing", ".vml")
./openpyxl-3.1.5.tar.gz: openpyxl-3.1.5/openpyxl/packaging/manifest.py: mimetypes.add_type("image/x-emf", ".emf")
./panel-1.5.3.tar.gz: panel-1.5.3/panel/io/resources.py: mimetypes.add_type("application/javascript", ".js")
./platformio-6.1.16.tar.gz: platformio-6.1.16/platformio/home/cli.py: mimetypes.add_type("text/html", ".html")
./platformio-6.1.16.tar.gz: platformio-6.1.16/platformio/home/cli.py: mimetypes.add_type("text/css", ".css")
./platformio-6.1.16.tar.gz: platformio-6.1.16/platformio/home/cli.py: mimetypes.add_type("application/javascript", ".js")
./nicegui-2.5.0.tar.gz: nicegui-2.5.0/nicegui/nicegui.py: mimetypes.add_type('text/javascript', '.js')
./nicegui-2.5.0.tar.gz: nicegui-2.5.0/nicegui/nicegui.py: mimetypes.add_type('text/css', '.css')
./robocorp_storage-1.0.5.tar.gz: robocorp_storage-1.0.5/src/robocorp/storage/__init__.py: mimetypes.add_type(type_, ext)
./prefect-3.1.0.tar.gz: prefect-3.1.0/src/prefect/server/api/server.py: mimetypes.add_type("application/javascript", ".js")
./streamlit-1.39.0.tar.gz: streamlit-1.39.0/streamlit/web/server/app_static_file_handler.py: mimetypes.add_type("image/webp", ".webp")
./streamlit-1.39.0.tar.gz: streamlit-1.39.0/streamlit/web/server/component_request_handler.py: mimetypes.add_type("text/html", ".html")
./streamlit-1.39.0.tar.gz: streamlit-1.39.0/streamlit/web/server/component_request_handler.py: mimetypes.add_type("application/javascript", ".js")
./streamlit-1.39.0.tar.gz: streamlit-1.39.0/streamlit/web/server/component_request_handler.py: mimetypes.add_type("text/css", ".css")
./supervisely-6.73.221.tar.gz: supervisely-6.73.221/supervisely/convert/image/image_converter.py: mimetypes.add_type("image/heic", ".heic")  # to extend types_map
./supervisely-6.73.221.tar.gz: supervisely-6.73.221/supervisely/convert/image/image_converter.py: mimetypes.add_type("image/heif", ".heif")  # to extend types_map
./supervisely-6.73.221.tar.gz: supervisely-6.73.221/supervisely/convert/image/image_converter.py: mimetypes.add_type("image/jpeg", ".jfif")  # to extend types_map
./supervisely-6.73.221.tar.gz: supervisely-6.73.221/supervisely/convert/image/image_converter.py: mimetypes.add_type("image/avif", ".avif")  # to extend types_map
./supervisely-6.73.221.tar.gz: supervisely-6.73.221/supervisely/convert/image/image_converter.py: mimetypes.add_type("image/bmp", ".bmp")  # to extend types_map
./supervisely-6.73.221.tar.gz: supervisely-6.73.221/supervisely/convert/image/image_helper.py: mimetypes.add_type("image/webp", ".webp")  # to extend types_map
./supervisely-6.73.221.tar.gz: supervisely-6.73.221/supervisely/convert/image/image_helper.py: mimetypes.add_type("image/jpeg", ".jfif")  # to extend types_map
./python_semantic_release-9.12.0.tar.gz: python_semantic_release-9.12.0/semantic_release/hvcs/github.py: mimetypes.add_type("application/octet-stream", ".whl")
./python_semantic_release-9.12.0.tar.gz: python_semantic_release-9.12.0/semantic_release/hvcs/github.py: mimetypes.add_type("text/markdown", ".md")
./sqlmesh-0.130.1.tar.gz: sqlmesh-0.130.1/web/server/main.py: mimetypes.add_type("application/javascript", ".js")
./sqlmesh-0.130.1.tar.gz: sqlmesh-0.130.1/web/server/main.py: mimetypes.add_type("text/css", ".css")
./trame-3.7.0.tar.gz: trame-3.7.0/trame/app/mimetypes.py: mimetypes.add_type(key, value)
./trame-3.7.0.tar.gz: trame-3.7.0/trame/app/mimetypes.py: mimetypes.add_type(type, ext)
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('image/png', '.png')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('image/jpeg', '.jpeg')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('image/webp', '.webp')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('image/gif', '.gif')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('image/bmp', '.bmp')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('image/x-tga', '.tga')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('image/tiff', '.tiff')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('image/vnd.adobe.photoshop', '.psd')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('video/mp4', '.mp4')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('video/quicktime', '.mov')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('video/avi', '.avi')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('audio/mpeg', '.mp3')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('audio/m4a', '.m4a')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('audio/aac', '.aac')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('audio/ogg', '.ogg')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('audio/flac', '.flac')
./Telethon-1.37.0.tar.gz: Telethon-1.37.0/telethon/utils.py: mimetypes.add_type('application/x-tgsticker', '.tgs')
./webob-1.8.9.tar.gz: webob-1.8.9/src/webob/static.py: mimetypes.add_type('text/javascript', '.js') # stdlib default is application/x-javascript
./webob-1.8.9.tar.gz: webob-1.8.9/src/webob/static.py: mimetypes.add_type('image/x-icon', '.ico') # not among defaults
./webob-1.8.9.tar.gz: webob-1.8.9/tests/test_request.py: mimetypes.add_type('application/x-foo', '.foo')
./pyvo-1.6.tar.gz: pyvo-1.6/pyvo/dal/mimetype.py: mimetypes.add_type('application/fits', 'fits')
./pyvo-1.6.tar.gz: pyvo-1.6/pyvo/dal/mimetype.py: mimetypes.add_type('application/x-fits', 'fits')
./pyvo-1.6.tar.gz: pyvo-1.6/pyvo/dal/mimetype.py: mimetypes.add_type('image/fits', 'fits')
./pyvo-1.6.tar.gz: pyvo-1.6/pyvo/dal/mimetype.py: mimetypes.add_type('text/plain', 'txt')

Time: 0:00:26.975038
Found 77 matching lines in 26 projects

Of the 77 calls (in 26 projects) to mimetypes.add_type:

68 are dotted
5 (in 4 projects) use a variable. I checked them and the variable uses dotted input.
4 (in 1 project) are undotted. I opened a PR: Add dot to extensions of added MIME types astropy/pyvo#622

gh-75223: Deprecate undotted extensions in `mimetypes.MimeTypes.add_t…

Deprecate in 3.14: gh-75223: Deprecate undotted extensions in mimetypes.MimeTypes.add_type #128638
Remove in 3.16

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mimetypes.add_type should complain when you give it an undotted ext #75223

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mimetypes.add_type should complain when you give it an undotted ext #75223

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OddBloke commented on Jul 25, 2017

jimjjewett commented on Nov 19, 2017

JulienPalard commented on Sep 13, 2019

JulienPalard commented on Sep 13, 2019

hugovk commented on Nov 21, 2024

hugovk commented on Apr 28, 2025

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