gh-145834: email.charset: remove viscii from CHARSETS — no Python codec exists

Lib/email/charset.py

@@ -50,7 +50,7 @@
     'iso-8859-15': (QP,        QP,      None),
     'iso-8859-16': (QP,        QP,      None),
     'windows-1252':(QP,        QP,      None),
-    'viscii':      (QP,        QP,      None),
+    # 'viscii' removed - no Python codec exists
     'us-ascii':    (None,      None,    None),
     'big5':        (BASE64,    BASE64,  None),
     'gb2312':      (BASE64,    BASE64,  None),

Lib/test/test_email/test_email.py

@@ -5008,6 +5008,29 @@ def test_unicode_charset_name(self):
         self.assertEqual(str(charset), 'us-ascii')
         self.assertRaises(errors.CharsetError, Charset, 'asc\xffii')
 
+    def test_viscii_not_registered(self):
+        # viscii has no Python codec, so it should not be in CHARSETS.
+        from email.charset import CHARSETS
+        self.assertNotIn('viscii', CHARSETS)
+
+    def test_all_charsets_have_codecs(self):
+        # Every charset registered in CHARSETS should have a resolvable
+        # Python codec (via CODEC_MAP or by name).
+        import codecs
+        from email.charset import CHARSETS, CODEC_MAP
+        for name in CHARSETS:
+            codec_name = CODEC_MAP.get(name, name)
+            if codec_name is None:
+                continue
+            with self.subTest(charset=name, codec=codec_name):
+                try:
+                    codecs.lookup(codec_name)
+                except LookupError:
+                    self.fail(
+                        f"charset {name!r} maps to codec {codec_name!r} "
+                        f"which is not available"
+                    )
+
 
 
 # Test multilingual MIME headers.

Misc/NEWS.d/next/Library/2026-03-11-15-59-25.gh-issue-145834._UxpJY.rst

@@ -0,0 +1,3 @@
+Remove ``viscii`` from :mod:`email.charset` ``CHARSETS`` table. Python has
+no ``viscii`` codec, so any encoding operation on ``Charset('viscii')``
+raised :exc:`LookupError`.