From d59a5e492be438a633930d955566cf224177aa57 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Mon, 1 Jun 2026 19:21:01 +0300
Subject: [PATCH] gh-93417: Add use_system_defaults option for mimetypes

---
 Lib/mimetypes.py           | 21 ++++++++++++---------
 Lib/test/test_mimetypes.py |  7 +++++++
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/Lib/mimetypes.py b/Lib/mimetypes.py
index 15e8c0a437bfd93..1085a669bf34a42 100644
--- a/Lib/mimetypes.py
+++ b/Lib/mimetypes.py
@@ -64,7 +64,7 @@ class MimeTypes:
     URL, and can guess a reasonable extension given a MIME type.
     """
 
-    def __init__(self, filenames=(), strict=True):
+    def __init__(self, filenames=(), strict=True, *, use_system_defaults=False):
         if not inited:
             init()
         self.encodings_map = _encodings_map_default.copy()
@@ -75,6 +75,14 @@ def __init__(self, filenames=(), strict=True):
             self.add_type(type, ext, True)
         for (ext, type) in _common_types_default.items():
             self.add_type(type, ext, False)
+        if use_system_defaults:
+            # Quick return if not supported
+            self.read_windows_registry(strict)
+            for name in knownfiles:
+                try:
+                    self.read(name, strict)
+                except OSError:
+                    pass
         for name in filenames:
             self.read(name, strict)
 
@@ -395,20 +403,15 @@ def add_type(type, ext, strict=True):
     return _db.add_type(type, ext, strict)
 
 
-def init(files=None):
+def init(files=None, *, use_system_defaults=True):
     global suffix_map, types_map, encodings_map, common_types
     global inited, _db
     inited = True    # so that MimeTypes.__init__() doesn't call us again
 
     if files is None or _db is None:
-        db = MimeTypes()
-        # Quick return if not supported
-        db.read_windows_registry()
-
+        db = MimeTypes(use_system_defaults=use_system_defaults)
         if files is None:
-            files = knownfiles
-        else:
-            files = knownfiles + list(files)
+            files = ()
     else:
         db = _db
 
diff --git a/Lib/test/test_mimetypes.py b/Lib/test/test_mimetypes.py
index 1a3b49b87b121f2..f97658fd86bf0ae 100644
--- a/Lib/test/test_mimetypes.py
+++ b/Lib/test/test_mimetypes.py
@@ -230,6 +230,9 @@ def test_init_knownfiles(self):
         mimetypes.init()
         self.assertEqual(guess_file_type("file.test2")[0], "testing/test2")
 
+        mimetypes.init(use_system_defaults=False)
+        self.assertEqual(guess_file_type("file.test2")[0], None)
+
     def test_added_types_are_used(self):
         mimetypes.add_type('testing/default-type', '')
         mime_type, _ = mimetypes.guess_type('')
@@ -272,6 +275,10 @@ def test_init_knownfiles(self):
         guess_file_type = db.guess_file_type
         self.assertEqual(guess_file_type("file.test2")[0], None)
 
+        db = mimetypes.MimeTypes(use_system_defaults=True)
+        guess_file_type = db.guess_file_type
+        self.assertEqual(guess_file_type("file.test2")[0], "testing/test2")
+
     def test_case_sensitivity(self):
         eq = self.assertEqual
         eq(self.db.guess_file_type("foobar.html"), ("text/html", None))