https://github.com/python/cpython/commit/46cff6be903165f723fb956bdce407de6b201acc
commit: 46cff6be903165f723fb956bdce407de6b201acc
branch: 3.13
author: Miss Islington (bot) <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2026-05-22T09:37:57Z
summary:

[3.13] gh-137571: Protect against possible UnboundLocalError in 
gzip._GzipReader.read() (GH-150222) (GH-150231)

This has not been observed in practice, but we cannot be 100% sure that
it will not happen with some weird gzip data.
(cherry picked from commit 28eac9a7263ad8dcfa9b536aa238549131857e0f)

Co-authored-by: Serhiy Storchaka <[email protected]>

files:
M Lib/gzip.py

diff --git a/Lib/gzip.py b/Lib/gzip.py
index a550c20a7a08ba..959c3cb58fdcd3 100644
--- a/Lib/gzip.py
+++ b/Lib/gzip.py
@@ -551,10 +551,10 @@ def read(self, size=-1):
             # Read a chunk of data from the file
             if self._decompressor.needs_input:
                 buf = self._fp.read(READ_BUFFER_SIZE)
-                uncompress = self._decompressor.decompress(buf, size)
             else:
-                uncompress = self._decompressor.decompress(b"", size)
+                buf = b""
 
+            uncompress = self._decompressor.decompress(buf, size)
             if self._decompressor.unused_data != b"":
                 # Prepend the already read bytes to the fileobj so they can
                 # be seen by _read_eof() and _read_gzip_header()

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