[Python-checkins] bpo-20392: Fix inconsistency with uppercase file extensions in mimetypes.guess_type (GH-30229)

[miss-islington]

https://github.com/python/cpython/commit/32ae9ab55f2cd97b5a28d5398c4820d8bc96f30c
commit: 32ae9ab55f2cd97b5a28d5398c4820d8bc96f30c
branch: 3.9
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: miss-islington <31488909+miss-islington at users.noreply.github.com>
date: 2022-03-15T08:50:01-07:00
summary:

bpo-20392: Fix inconsistency with uppercase file extensions in mimetypes.guess_type (GH-30229)

(cherry picked from commit 5dd7ec52b83e7f239774cf7478106fcc7b0a36f3)

Co-authored-by: Kumar Aditya <59607654+kumaraditya303 at users.noreply.github.com>

files:
A Misc/NEWS.d/next/Library/2021-12-22-12-02-27.bpo-20392.CLAFIp.rst
M Lib/mimetypes.py
M Lib/test/test_mimetypes.py

diff --git a/Lib/mimetypes.py b/Lib/mimetypes.py
index d36e1664cdcc8..58ace01b41ab1 100644
--- a/Lib/mimetypes.py
+++ b/Lib/mimetypes.py
@@ -135,25 +135,23 @@ def guess_type(self, url, strict=True):
                 type = 'text/plain'
             return type, None           # never compressed, so encoding is None
         base, ext = posixpath.splitext(url)
-        while ext in self.suffix_map:
-            base, ext = posixpath.splitext(base + self.suffix_map[ext])
+        while (ext_lower := ext.lower()) in self.suffix_map:
+            base, ext = posixpath.splitext(base + self.suffix_map[ext_lower])
+        # encodings_map is case sensitive
         if ext in self.encodings_map:
             encoding = self.encodings_map[ext]
             base, ext = posixpath.splitext(base)
         else:
             encoding = None
+        ext = ext.lower()
         types_map = self.types_map[True]
         if ext in types_map:
             return types_map[ext], encoding
-        elif ext.lower() in types_map:
-            return types_map[ext.lower()], encoding
         elif strict:
             return None, encoding
         types_map = self.types_map[False]
         if ext in types_map:
             return types_map[ext], encoding
-        elif ext.lower() in types_map:
-            return types_map[ext.lower()], encoding
         else:
             return None, encoding
 
diff --git a/Lib/test/test_mimetypes.py b/Lib/test/test_mimetypes.py
index 5d0615e99b4e4..254b8f8a4aeb7 100644
--- a/Lib/test/test_mimetypes.py
+++ b/Lib/test/test_mimetypes.py
@@ -27,6 +27,13 @@ def tearDownModule():
 class MimeTypesTestCase(unittest.TestCase):
     def setUp(self):
         self.db = mimetypes.MimeTypes()
+        
+    def test_case_sensitivity(self):
+        eq = self.assertEqual
+        eq(self.db.guess_type("foobar.HTML"), self.db.guess_type("foobar.html"))
+        eq(self.db.guess_type("foobar.TGZ"), self.db.guess_type("foobar.tgz"))
+        eq(self.db.guess_type("foobar.tar.Z"), ("application/x-tar", "compress"))
+        eq(self.db.guess_type("foobar.tar.z"), (None, None))
 
     def test_default_data(self):
         eq = self.assertEqual
diff --git a/Misc/NEWS.d/next/Library/2021-12-22-12-02-27.bpo-20392.CLAFIp.rst b/Misc/NEWS.d/next/Library/2021-12-22-12-02-27.bpo-20392.CLAFIp.rst
new file mode 100644
index 0000000000000..8973c4d433174
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-12-22-12-02-27.bpo-20392.CLAFIp.rst
@@ -0,0 +1 @@
+Fix inconsistency with uppercase file extensions in :meth:`MimeTypes.guess_type`. Patch by Kumar Aditya.