https://github.com/python/cpython/commit/a7bf27f7f521384a8964718bdb58a5cb113bb3ec
commit: a7bf27f7f521384a8964718bdb58a5cb113bb3ec
branch: main
author: Benel Tayar <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2025-11-07T10:47:25Z
summary:
gh-141141: Make base64.b85decode() thread safe (GH-141149)
files:
A Misc/NEWS.d/next/Library/2025-11-06-15-11-50.gh-issue-141141.tgIfgH.rst
M Lib/base64.py
diff --git a/Lib/base64.py b/Lib/base64.py
index 5d78cc09f40cd3..cfc57626c40ba9 100644
--- a/Lib/base64.py
+++ b/Lib/base64.py
@@ -462,9 +462,12 @@ def b85decode(b):
# Delay the initialization of tables to not waste memory
# if the function is never called
if _b85dec is None:
- _b85dec = [None] * 256
+ # we don't assign to _b85dec directly to avoid issues when
+ # multiple threads call this function simultaneously
+ b85dec_tmp = [None] * 256
for i, c in enumerate(_b85alphabet):
- _b85dec[c] = i
+ b85dec_tmp[c] = i
+ _b85dec = b85dec_tmp
b = _bytes_from_decode_data(b)
padding = (-len(b)) % 5
diff --git
a/Misc/NEWS.d/next/Library/2025-11-06-15-11-50.gh-issue-141141.tgIfgH.rst
b/Misc/NEWS.d/next/Library/2025-11-06-15-11-50.gh-issue-141141.tgIfgH.rst
new file mode 100644
index 00000000000000..f59ccfb33e7669
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-11-06-15-11-50.gh-issue-141141.tgIfgH.rst
@@ -0,0 +1 @@
+Fix a thread safety issue with :func:`base64.b85decode`. Contributed by Benel
Tayar.
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