commit daef21ce7dfd3735101d85d6ebf7554187c33ab8
author Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> Mon Feb 24 19:42:39 2020 -0800
committer GitHub <noreply@github.com> Tue Feb 25 06:42:39 2020 +0300
tree 5d82af9309af1da8df7a385e2e2b1692e5f0cf0f
parent 1f4cf0c22b00fefb17611546755b65d3cb488330

bpo-30566: Fix IndexError when using punycode codec (GH-18632)

Trying to decode an invalid string with the punycode codec
shoud raise UnicodeError.

(cherry picked from commit ba22e8f174309979d90047c5dc64fcb63bc2c32e)

Co-authored-by: Berker Peksag <berker.peksag@gmail.com>

Lib/encodings/punycode.py

diff --git a/Lib/encodings/punycode.py b/Lib/encodings/punycode.py
index 66c5101..1c57264 100644
--- a/Lib/encodings/punycode.py
+++ b/Lib/encodings/punycode.py
@@ -143,7 +143,7 @@
             digit = char - 22 # 0x30-26
         elif errors == "strict":
             raise UnicodeError("Invalid extended code point '%s'"
-                               % extended[extpos])
+                               % extended[extpos-1])
         else:
             return extpos, None
         t = T(j, bias)