From 58f3fe0d9b9882656e629e8caab687c7fcb21b36 Mon Sep 17 00:00:00 2001
From: Cody Maloney <cmaloney@users.noreply.github.com>
Date: Tue, 18 Nov 2025 01:10:32 -0800
Subject: [PATCH] gh-129005: Remove copies from _pyio using take_bytes
 (#141539)

Memory usage now matches that of _io for large files.
---
 Lib/_pyio.py                        | 8 ++++----
 Lib/test/test_io/test_bufferedio.py | 3 ++-
 Lib/test/test_io/test_largefile.py  | 6 ++----
 3 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 423178e87a86..69a088df8fc9 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -546,7 +546,7 @@ class IOBase(metaclass=abc.ABCMeta):
             res += b
             if res.endswith(b"\n"):
                 break
-        return bytes(res)
+        return res.take_bytes()
 
     def __iter__(self):
         self._checkClosed()
@@ -620,7 +620,7 @@ class RawIOBase(IOBase):
         if n < 0 or n > len(b):
             raise ValueError(f"readinto returned {n} outside buffer size {len(b)}")
         del b[n:]
-        return bytes(b)
+        return b.take_bytes()
 
     def readall(self):
         """Read until EOF, using multiple read() call."""
@@ -628,7 +628,7 @@ class RawIOBase(IOBase):
         while data := self.read(DEFAULT_BUFFER_SIZE):
             res += data
         if res:
-            return bytes(res)
+            return res.take_bytes()
         else:
             # b'' or None
             return data
@@ -1738,7 +1738,7 @@ class FileIO(RawIOBase):
         assert len(result) - bytes_read >= 1, \
             "os.readinto buffer size 0 will result in erroneous EOF / returns 0"
         result.resize(bytes_read)
-        return bytes(result)
+        return result.take_bytes()
 
     def readinto(self, buffer):
         """Same as RawIOBase.readinto()."""
diff --git a/Lib/test/test_io/test_bufferedio.py b/Lib/test/test_io/test_bufferedio.py
index 30c34e818b15..3278665bdc9d 100644
--- a/Lib/test/test_io/test_bufferedio.py
+++ b/Lib/test/test_io/test_bufferedio.py
@@ -1277,7 +1277,8 @@ class BufferedRandomTest(BufferedReaderTest, BufferedWriterTest):
         def _readinto(bufio, n=-1):
             b = bytearray(n if n >= 0 else 9999)
             n = bufio.readinto(b)
-            return bytes(b[:n])
+            b.resize(n)
+            return b.take_bytes()
         self.check_flush_and_read(_readinto)
 
     def test_flush_and_peek(self):
diff --git a/Lib/test/test_io/test_largefile.py b/Lib/test/test_io/test_largefile.py
index 41f7b70e5cfe..438a90a92ed5 100644
--- a/Lib/test/test_io/test_largefile.py
+++ b/Lib/test/test_io/test_largefile.py
@@ -56,9 +56,7 @@ class TestFileMethods(LargeFileTest):
     (i.e. > 2 GiB) files.
     """
 
-    # _pyio.FileIO.readall() uses a temporary bytearray then casted to bytes,
-    # so memuse=2 is needed
-    @bigmemtest(size=size, memuse=2, dry_run=False)
+    @bigmemtest(size=size, memuse=1, dry_run=False)
     def test_large_read(self, _size):
         # bpo-24658: Test that a read greater than 2GB does not fail.
         with self.open(TESTFN, "rb") as f:
@@ -154,7 +152,7 @@ class TestFileMethods(LargeFileTest):
                 f.seek(pos)
                 self.assertTrue(f.seekable())
 
-    @bigmemtest(size=size, memuse=2, dry_run=False)
+    @bigmemtest(size=size, memuse=1, dry_run=False)
     def test_seek_readall(self, _size):
         # Seek which doesn't change position should readall successfully.
         with self.open(TESTFN, 'rb') as f:
-- 
2.47.3