From c30cfeeafd2e762ed22d1a9502539e00ddc9c200 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Mon, 6 Apr 2026 11:29:33 +0300
Subject: [PATCH] gh-148153: Do not use assert for parameter validation in
 base64

base64.b32encode() now always raises ValueError instead of
AssertionError for the value of map01 with invalid length.
---
 Doc/library/base64.rst                                       | 3 ---
 Lib/base64.py                                                | 1 -
 Lib/test/test_base64.py                                      | 5 +++++
 .../Library/2026-04-06-11-20-24.gh-issue-148153.ZtsuTl.rst   | 2 ++
 4 files changed, 7 insertions(+), 4 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2026-04-06-11-20-24.gh-issue-148153.ZtsuTl.rst

diff --git a/Doc/library/base64.rst b/Doc/library/base64.rst
index 425dff8f2a9ad1..6e6e5d603e37b1 100644
--- a/Doc/library/base64.rst
+++ b/Doc/library/base64.rst
@@ -69,9 +69,6 @@ POST request.
    after at most every *wrapcol* characters.
    If *wrapcol* is zero (default), do not insert any newlines.
 
-   May assert or raise a :exc:`ValueError` if the length of *altchars* is not 2.  Raises a
-   :exc:`TypeError` if *altchars* is not a :term:`bytes-like object`.
-
    .. versionchanged:: 3.15
       Added the *padded* and *wrapcol* parameters.
 
diff --git a/Lib/base64.py b/Lib/base64.py
index a94bec4d031c52..7f39c68070b5da 100644
--- a/Lib/base64.py
+++ b/Lib/base64.py
@@ -237,7 +237,6 @@ def b32decode(s, casefold=False, map01=None, *, padded=True, ignorechars=b''):
     # either L (el) or I (eye).
     if map01 is not None:
         map01 = _bytes_from_decode_data(map01)
-        assert len(map01) == 1, repr(map01)
         s = s.translate(bytes.maketrans(b'01', b'O' + map01))
     if casefold:
         s = s.upper()
diff --git a/Lib/test/test_base64.py b/Lib/test/test_base64.py
index 1a4dd56a553f4d..868abcfee24e10 100644
--- a/Lib/test/test_base64.py
+++ b/Lib/test/test_base64.py
@@ -607,6 +607,11 @@ def test_b32decode_map01(self):
         self.assertRaises(binascii.Error, base64.b32decode, b'M1O23456')
         self.assertRaises(binascii.Error, base64.b32decode, b'ML023456')
         self.assertRaises(binascii.Error, base64.b32decode, b'MI023456')
+        self.assertRaises(ValueError, base64.b32decode, b'', map01=b'')
+        self.assertRaises(ValueError, base64.b32decode, b'', map01=b'LI')
+        self.assertRaises(TypeError, base64.b32decode, b'', map01=0)
+        eq(base64.b32decode(b'MLO23456', map01=None), res_L)
+        self.assertRaises(binascii.Error, base64.b32decode, b'M1023456', map01=None)
 
         data = b'M1023456'
         data_str = data.decode('ascii')
diff --git a/Misc/NEWS.d/next/Library/2026-04-06-11-20-24.gh-issue-148153.ZtsuTl.rst b/Misc/NEWS.d/next/Library/2026-04-06-11-20-24.gh-issue-148153.ZtsuTl.rst
new file mode 100644
index 00000000000000..7fd30562739fee
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-04-06-11-20-24.gh-issue-148153.ZtsuTl.rst
@@ -0,0 +1,2 @@
+:func:`base64.b32encode` now always raises :exc:`ValueError` instead of
+:exc:`AssertionError` for the value of *map01* with invalid length.