gh-92455: Respect case-sensitive mimetype suffixes by yuanx749 · Pull Request #148782 · python/cpython

yuanx749 · 2026-04-19T22:12:12Z

As described in the issue, the current implementation cannot find uppercase
extensions added via mimetypes.add_type(). This appears to be a regression from gh-30229.

This restores the lookup order documented for mimetypes.guess_type():
type suffixes are tried case-sensitively first, then case-insensitively.

…sensitive-add-type

ifrh

I cannot approve the changes formaly, but they look good for me.

serhiy-storchaka · 2026-05-31T21:44:49Z

        eq(self.db.guess_type("scheme:foobar.tar.z"), (None, None))

+    def test_added_types_case_sensitive_preferred(self):
+        self.db.add_type("text/x-r-script", ".R")


"text/x-r-script" could be added to the database in future. It is better to use something less likely to be added.

Please add also tests for strict=False.

Thanks for the review. I changed the test type and added tests for strict=False.

serhiy-storchaka · 2026-06-01T07:10:29Z

#30229 changed also the code related to suffix_map. I wonder if it needs correction too:

        while True:
            if ext in self.suffix_map:
                base, ext = posixpath.splitext(base + self.suffix_map[ext])
                continue
            ext_lower = ext.lower():
            if ext_lower in self.suffix_map:
                base, ext = posixpath.splitext(base + self.suffix_map[ext_lower])
                continue
            break

@kumaraditya303, what are your thoughts?

…sensitive-add-type # Conflicts: # Lib/test/test_mimetypes.py

kumaraditya303 · 2026-06-05T08:58:29Z

what are your thoughts?

I think we should do the same for suffix_map i.e. first try case sensitively then case-insensitively.

…sensitive-add-type

yuanx749 · 2026-06-06T19:00:15Z

Would you prefer handling suffix_map in this PR, or keeping this focused on types_map?

serhiy-storchaka · 2026-06-06T21:18:45Z

It is better to handle all in one PR. Also please update the documentation.

…sensitive-add-type

yuanx749 · 2026-06-08T09:07:23Z

Added a failing test, then updated suffix_map to try the original suffix before the lower case suffix. I also updated the documentation. The existing strict=False lookup order is unchanged.

read-the-docs-community · 2026-06-08T09:07:36Z

Documentation build overview

📚 cpython-previews | 🛠️ Build #33136408 | 📁 Comparing 44a5da7 against main (8276778)

🔍 Preview build

216 files changed · + 6 added · ± 210 modified

+ Added

± Modified

…sensitive-add-type

serhiy-storchaka

There are open questions: Should we try case-sensitive in non-strict mapping before case-insensitive in strict mapping? What to do with asymmetry in registering upper-case and lower-case extensions? I do not see clear answers on them, so we can leave them to other issues (when we get clear answers).

I think that the documentation for add_type() should be updated. Registered lower-case extensions will match any case.

…sensitive-add-type

yuanx749 · 2026-06-14T17:01:36Z

There are open questions: Should we try case-sensitive in non-strict mapping before case-insensitive in strict mapping? What to do with asymmetry in registering upper-case and lower-case extensions? I do not see clear answers on them, so we can leave them to other issues (when we get clear answers).

I think that the documentation for add_type() should be updated. Registered lower-case extensions will match any case.

The original lookup behavior is now preserved. I have also updated the add_type() and MimeTypes.add_type() docstrings and the corresponding documentation.

serhiy-storchaka

LGTM. 👍

…sensitive-add-type

bedevere-bot · 2026-06-15T16:32:21Z

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot aarch64 Android 3.x (tier-3) has failed when building commit 46107ad.

What do you need to do:

Don't panic.
Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1594/builds/5095) and take a look at the build logs.
Check if the failure is related to this commit (46107ad) or if it is a false positive.
If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1594/builds/5095

Failed tests:

test_urllib2
test_urllibnet

Failed subtests:

test_ftp_error - test.test_urllib2.HandlerTests.test_ftp_error
test_getcode - test.test_urllibnet.urlopenNetworkTests.test_getcode

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/urllib/request.py", line 1531, in ftp_open
    host = socket.gethostbyname(host)
socket.gaierror: [Errno 7] No address associated with hostname
 
During handling of the above exception, another exception occurred:
 
Traceback (most recent call last):
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/test/test_urllib2.py", line 815, in test_ftp_error
    urlopen("ftp://www.pythontest.net/")
    ~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/urllib/request.py", line 489, in open
    response = self._open(req, data)
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/urllib/request.py", line 506, in _open
    result = self._call_chain(self.handle_open, protocol, protocol +
                              '_open', req)
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/urllib/request.py", line 466, in _call_chain
    result = func(*args)
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/urllib/request.py", line 1533, in ftp_open
    raise URLError(msg)
urllib.error.URLError: <urlopen error [Errno 7] No address associated with hostname>
 
During handling of the above exception, another exception occurred:
 
Traceback (most recent call last):
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/test/test_urllib2.py", line 817, in test_ftp_error
    self.assertEqual(raised.reason,
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
                     f"ftp error: {exception.args[0]}")
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: gaierror(7, 'No address associated with hostname') != 'ftp error: 500 OOPS: cannot change directory:/nonexistent'
 
----------------------------------------------------------------------
Ran 81 tests in 0.074s
 
FAILED (failures=1, skipped=3)


Traceback (most recent call last):
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/urllib/request.py", line 1531, in ftp_open
    host = socket.gethostbyname(host)
socket.gaierror: [Errno 7] No address associated with hostname
 
During handling of the above exception, another exception occurred:
 
Traceback (most recent call last):
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/test/test_urllib2.py", line 815, in test_ftp_error
    urlopen("ftp://www.pythontest.net/")
    ~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/urllib/request.py", line 489, in open
    response = self._open(req, data)
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/urllib/request.py", line 506, in _open
    result = self._call_chain(self.handle_open, protocol, protocol +
                              '_open', req)
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/urllib/request.py", line 466, in _call_chain
    result = func(*args)
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/urllib/request.py", line 1533, in ftp_open
    raise URLError(msg)
urllib.error.URLError: <urlopen error [Errno 7] No address associated with hostname>
 
During handling of the above exception, another exception occurred:
 
Traceback (most recent call last):
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/test/test_urllib2.py", line 817, in test_ftp_error
    self.assertEqual(raised.reason,
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
                     f"ftp error: {exception.args[0]}")
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: gaierror(7, 'No address associated with hostname') != 'ftp error: 500 OOPS: cannot change directory:/nonexistent'
 
----------------------------------------------------------------------
Ran 81 tests in 0.050s
 
FAILED (failures=1, skipped=3)


Traceback (most recent call last):
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/test/test_urllibnet.py", line 107, in test_getcode
    self.assertEqual(e.exception.code, 404)
                     ^^^^^^^^^^^^^^^^
AttributeError: 'URLError' object has no attribute 'code'
 
----------------------------------------------------------------------
Ran 12 tests in 0.034s
 
FAILED (errors=1, skipped=10)


Traceback (most recent call last):
  File "/data/user/0/org.python.testbed/files/python/lib/python3.16/test/test_urllibnet.py", line 107, in test_getcode
    self.assertEqual(e.exception.code, 404)
                     ^^^^^^^^^^^^^^^^
AttributeError: 'URLError' object has no attribute 'code'
 
----------------------------------------------------------------------
Ran 12 tests in 0.031s
 
FAILED (errors=1, skipped=10)

…8782)

pythongh-92455: Respect case-sensitive mimetype suffixes

2720dbd

yuanx749 requested a review from a team as a code owner April 19, 2026 22:12

bedevere-app Bot added the awaiting review label Apr 19, 2026

bedevere-app Bot mentioned this pull request Apr 19, 2026

mimetypes.guess_type could not find mimetypes added by mimetypes.add_type i.e. in PY3.10.4 // OR : different return values (PY2.7 to PY3.9.7) vs (PY3.9.11 to PY3.10.4) #92455

Closed

yuanx749 added 4 commits April 20, 2026 01:26

Add NEWS entry

547a64e

Merge remote-tracking branch 'upstream/main' into fix-mimetypes-case-…

992a6e3

…sensitive-add-type

Merge remote-tracking branch 'upstream/main' into fix-mimetypes-case-…

561a0aa

…sensitive-add-type

Merge remote-tracking branch 'upstream/main' into fix-mimetypes-case-…

90b7360

…sensitive-add-type

ifrh reviewed May 26, 2026

View reviewed changes

serhiy-storchaka reviewed May 31, 2026

View reviewed changes

serhiy-storchaka requested a review from kumaraditya303 June 1, 2026 07:04

yuanx749 added 3 commits June 3, 2026 19:41

Merge remote-tracking branch 'upstream/main' into fix-mimetypes-case-…

268d57c

…sensitive-add-type # Conflicts: # Lib/test/test_mimetypes.py

Add non-strict mimetype case test

47b2b6b

Merge branch 'main' into fix-mimetypes-case-sensitive-add-type

fe1096a

yuanx749 added 2 commits June 6, 2026 21:44

Test strict lookup excludes non-strict types

e554892

Merge remote-tracking branch 'upstream/main' into fix-mimetypes-case-…

3085bb9

…sensitive-add-type

yuanx749 added 4 commits June 8, 2026 11:37

Test suffix map case lookup

206be36

Respect suffix map case lookup

6f639f2

Document mimetypes case lookup

4886f13

Merge remote-tracking branch 'upstream/main' into fix-mimetypes-case-…

046dc95

…sensitive-add-type

yuanx749 added 3 commits June 8, 2026 13:24

Merge remote-tracking branch 'upstream/main' into fix-mimetypes-case-…

430a329

…sensitive-add-type

Merge branch 'main' into fix-mimetypes-case-sensitive-add-type

2ed828a

Merge remote-tracking branch 'upstream/main' into fix-mimetypes-case-…

50552fa

…sensitive-add-type

yuanx749 requested a review from serhiy-storchaka June 14, 2026 15:58

serhiy-storchaka reviewed Jun 14, 2026

View reviewed changes

yuanx749 added 2 commits June 14, 2026 19:54

Update documentation

0874c07

Merge remote-tracking branch 'upstream/main' into fix-mimetypes-case-…

5c56f96

…sensitive-add-type

serhiy-storchaka approved these changes Jun 14, 2026

View reviewed changes

bedevere-app Bot added awaiting merge and removed awaiting review labels Jun 14, 2026

Merge remote-tracking branch 'upstream/main' into fix-mimetypes-case-…

44a5da7

…sensitive-add-type

serhiy-storchaka enabled auto-merge (squash) June 15, 2026 14:42

serhiy-storchaka merged commit 46107ad into python:main Jun 15, 2026
93 of 95 checks passed

bedevere-app Bot removed the awaiting merge label Jun 15, 2026

yuanx749 deleted the fix-mimetypes-case-sensitive-add-type branch June 15, 2026 15:15

philthompson10 pushed a commit to philthompson10/cpython that referenced this pull request Jun 17, 2026

pythongh-92455: Respect case-sensitive mimetype suffixes (pythonGH-14…

9c9ad0f

…8782)

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