From: Cody Maloney <cmaloney@users.noreply.github.com>
Date: Thu, 6 Feb 2025 10:18:08 +0000 (-0800)
Subject: gh-129005: Update _pyio.BytesIO to use bytearray.resize on write (#129702)
X-Git-Tag: v3.14.0a5~96
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=052ca8ffe8c57afb9c270fcc4eb5f390cbcfb8ce;p=thirdparty%2FPython%2Fcpython.git

gh-129005: Update _pyio.BytesIO to use bytearray.resize on write (#129702)

Co-authored-by: Victor Stinner <vstinner@python.org>
---

diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 023478aa78c6..b3a8f37d68ac 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -937,10 +937,8 @@ class BytesIO(BufferedIOBase):
             return 0
         pos = self._pos
         if pos > len(self._buffer):
-            # Inserts null bytes between the current end of the file
-            # and the new write position.
-            padding = b'\x00' * (pos - len(self._buffer))
-            self._buffer += padding
+            # Pad buffer to pos with null bytes.
+            self._buffer.resize(pos)
         self._buffer[pos:pos + n] = b
         self._pos += n
         return n