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gh-159191: Add a fast path to bytes.join() for exact bytes items #159096

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gh-159191: Add a fast path to bytes.join() for exact bytes items #159096

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2b106e5
gh-158803: Borrow bytes items in bytes.join() while the list is locked
christianaurichzm Oct 8, 2026
ad4a180
gh-158803: Copy exact bytes items directly in bytes.join()
christianaurichzm Oct 11, 2026
e73c74c
gh-159191: Move the NEWS entry to the new issue
christianaurichzm Oct 11, 2026
6794be4
gh-159191: Stress test bytes.join() with non-bytes items
christianaurichzm Oct 12, 2026
ec07466
gh-159191: Explain the bytes shortcut in the buffer cleanup loop
christianaurichzm Oct 13, 2026
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gh-159191: Stress test bytes.join() with non-bytes items 
The existing stress tests now only take the fast path. test_bytes is
part of the PGO training set, so the general path was barely trained,
and PGO builds stopped inlining PyBuffer_Release() there: joining a
list that is half bytearrays became about 14% slower than on main.
With this test it is back to main's speed.
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christianaurichzm committed Oct 12, 2026
commit 6794be4952ab29969778bbcdba1c0df7a50aaf3f
2 changes: 2 additions & 0 deletions Lib/test/test_bytes.py
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Expand Up @@ -655,6 +655,8 @@ def test_join(self):
seq = [b"abc"] * 100000
expected = b"abc" + b".:abc" * 99999
self.assertEqual(dot_join(seq), expected)
seq = [bytearray(b"abc")] * 100000
self.assertEqual(dot_join(seq), expected)
# Stress test with empty separator
seq = [b"abc"] * 100000
expected = b"abc" * 100000
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