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gh-139871: Add `bytearray.take_bytes([n])` to efficiently extract `bytes` by cmaloney · Pull Request #140128 · python/cpython

This sets up so the bytes can be "taken" as a byes object without
requiring a copy.

I ran pyperformance (results below) and don't see any major speedups
or slowdowns with this; all seems to be in the noise of my machine.

------

pyperformance compare main.json bytearray_bytes.json -O table
main.json
=========

Performance version: 1.11.0
Report on Linux-6.17.1-arch1-1-x86_64-with-glibc2.42
Number of logical CPUs: 32
Start date: 2025-10-14 00:55:52.519236
End date: 2025-10-14 02:23:01.308400

bytearray_bytes.json
====================

Performance version: 1.11.0
Report on Linux-6.17.1-arch1-1-x86_64-with-glibc2.42
Number of logical CPUs: 32
Start date: 2025-10-13 23:22:29.928152
End date: 2025-10-14 00:49:34.467284

+----------------------------------+-----------+----------------------+--------------+------------------------+
| Benchmark                        | main.json | bytearray_bytes.json | Change       | Significance           |
+==================================+===========+======================+==============+========================+
| 2to3                             | 137 ms    | 136 ms               | 1.00x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_generators                 | 193 ms    | 195 ms               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_cpu_io_mixed          | 285 ms    | 286 ms               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_cpu_io_mixed_tg       | 289 ms    | 290 ms               | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_eager                 | 50.4 ms   | 51.5 ms              | 1.02x slower | Significant (t=-10.40) |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_eager_cpu_io_mixed    | 223 ms    | 225 ms               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_eager_cpu_io_mixed_tg | 263 ms    | 264 ms               | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_eager_io              | 370 ms    | 372 ms               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_eager_io_tg           | 380 ms    | 384 ms               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_eager_memoization     | 125 ms    | 126 ms               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_eager_memoization_tg  | 161 ms    | 162 ms               | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_eager_tg              | 125 ms    | 125 ms               | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_io                    | 366 ms    | 360 ms               | 1.02x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_io_tg                 | 359 ms    | 361 ms               | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_memoization           | 177 ms    | 181 ms               | 1.02x slower | Significant (t=-9.20)  |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_memoization_tg        | 188 ms    | 189 ms               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_none                  | 151 ms    | 151 ms               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| async_tree_none_tg               | 150 ms    | 151 ms               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| asyncio_tcp                      | 182 ms    | 161 ms               | 1.13x faster | Significant (t=32.85)  |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| asyncio_tcp_ssl                  | 548 ms    | 553 ms               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| asyncio_websockets               | 342 ms    | 339 ms               | 1.01x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| bench_mp_pool                    | 7.12 ms   | 7.08 ms              | 1.01x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| bench_thread_pool                | 818 us    | 819 us               | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| bpe_tokeniser                    | 2.10 sec  | 2.09 sec             | 1.00x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| chaos                            | 27.9 ms   | 28.0 ms              | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| comprehensions                   | 7.45 us   | 7.24 us              | 1.03x faster | Significant (t=3.27)   |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| connected_components             | 308 ms    | 309 ms               | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| coroutines                       | 11.1 ms   | 11.2 ms              | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| coverage                         | 33.6 ms   | 34.1 ms              | 1.02x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| create_gc_cycles                 | 1.16 ms   | 1.16 ms              | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| crypto_pyaes                     | 37.1 ms   | 35.6 ms              | 1.04x faster | Significant (t=10.63)  |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| dask                             | 347 ms    | 351 ms               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| deepcopy                         | 118 us    | 117 us               | 1.00x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| deepcopy_memo                    | 12.8 us   | 12.7 us              | 1.00x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| deepcopy_reduce                  | 1.32 us   | 1.34 us              | 1.02x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| deltablue                        | 1.65 ms   | 1.64 ms              | 1.01x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| django_template                  | 17.9 ms   | 17.8 ms              | 1.00x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| docutils                         | 1.19 sec  | 1.20 sec             | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| dulwich_log                      | 19.5 ms   | 19.7 ms              | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| fannkuch                         | 184 ms    | 181 ms               | 1.02x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| float                            | 37.1 ms   | 36.7 ms              | 1.01x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| gc_traversal                     | 3.04 ms   | 2.84 ms              | 1.07x faster | Significant (t=19.48)  |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| generators                       | 15.9 ms   | 15.3 ms              | 1.04x faster | Significant (t=7.03)   |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| genshi_text                      | 11.3 ms   | 11.2 ms              | 1.01x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| genshi_xml                       | 25.5 ms   | 25.5 ms              | 1.00x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| go                               | 57.6 ms   | 56.7 ms              | 1.02x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| hexiom                           | 2.92 ms   | 2.88 ms              | 1.02x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| html5lib                         | 26.0 ms   | 26.5 ms              | 1.02x slower | Significant (t=-9.20)  |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| json_dumps                       | 4.48 ms   | 4.44 ms              | 1.01x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| json_loads                       | 11.7 us   | 11.7 us              | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| k_core                           | 1.41 sec  | 1.42 sec             | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| logging_format                   | 3.27 us   | 3.30 us              | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| logging_silent                   | 45.5 ns   | 45.8 ns              | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| logging_simple                   | 3.02 us   | 3.01 us              | 1.00x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| mako                             | 6.02 ms   | 6.03 ms              | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| many_optionals                   | 473 us    | 478 us               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| mdp                              | 587 ms    | 578 ms               | 1.02x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| meteor_contest                   | 50.2 ms   | 50.5 ms              | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| nbody                            | 54.6 ms   | 52.4 ms              | 1.04x faster | Significant (t=10.72)  |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| nqueens                          | 41.7 ms   | 40.4 ms              | 1.03x faster | Significant (t=6.79)   |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| pathlib                          | 9.77 ms   | 9.73 ms              | 1.00x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| pickle                           | 5.99 us   | 6.01 us              | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| pickle_dict                      | 12.5 us   | 12.8 us              | 1.02x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| pickle_list                      | 1.98 us   | 1.96 us              | 1.01x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| pickle_pure_python               | 149 us    | 150 us               | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| pidigits                         | 111 ms    | 115 ms               | 1.03x slower | Significant (t=-18.53) |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| pprint_pformat                   | 737 ms    | 748 ms               | 1.02x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| pprint_safe_repr                 | 362 ms    | 369 ms               | 1.02x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| pyflate                          | 211 ms    | 205 ms               | 1.03x faster | Significant (t=7.43)   |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| python_startup                   | 7.88 ms   | 7.88 ms              | 1.00x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| python_startup_no_site           | 4.72 ms   | 4.76 ms              | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| raytrace                         | 130 ms    | 128 ms               | 1.02x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| regex_compile                    | 50.0 ms   | 50.2 ms              | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| regex_dna                        | 101 ms    | 103 ms               | 1.02x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| regex_effbot                     | 1.72 ms   | 1.77 ms              | 1.03x slower | Significant (t=-26.42) |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| regex_v8                         | 12.5 ms   | 12.3 ms              | 1.02x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| richards                         | 20.4 ms   | 20.0 ms              | 1.02x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| richards_super                   | 23.4 ms   | 22.8 ms              | 1.03x faster | Significant (t=11.36)  |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| scimark_fft                      | 154 ms    | 153 ms               | 1.00x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| scimark_lu                       | 55.4 ms   | 57.0 ms              | 1.03x slower | Significant (t=-5.67)  |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| scimark_monte_carlo              | 32.8 ms   | 32.8 ms              | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| scimark_sor                      | 57.8 ms   | 56.9 ms              | 1.02x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| scimark_sparse_mat_mult          | 2.75 ms   | 2.76 ms              | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| shortest_path                    | 316 ms    | 318 ms               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| spectral_norm                    | 47.7 ms   | 51.6 ms              | 1.08x slower | Significant (t=-2.01)  |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| sphinx                           | 465 ms    | 467 ms               | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| sqlglot_v2_normalize             | 50.3 ms   | 50.2 ms              | 1.00x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| sqlglot_v2_optimize              | 24.2 ms   | 24.4 ms              | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| sqlglot_v2_parse                 | 576 us    | 572 us               | 1.01x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| sqlglot_v2_transpile             | 724 us    | 722 us               | 1.00x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| sqlite_synth                     | 1.14 us   | 1.15 us              | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| subparsers                       | 20.6 ms   | 20.7 ms              | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| sympy_expand                     | 181 ms    | 184 ms               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| sympy_integrate                  | 8.54 ms   | 8.55 ms              | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| sympy_str                        | 103 ms    | 105 ms               | 1.02x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| sympy_sum                        | 55.9 ms   | 56.0 ms              | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| telco                            | 3.39 ms   | 3.34 ms              | 1.01x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| tomli_loads                      | 971 ms    | 982 ms               | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| typing_runtime_protocols         | 73.2 us   | 73.6 us              | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| unpack_sequence                  | 25.2 ns   | 23.0 ns              | 1.10x faster | Significant (t=7.03)   |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| unpickle                         | 6.99 us   | 7.05 us              | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| unpickle_list                    | 2.07 us   | 2.10 us              | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| unpickle_pure_python             | 105 us    | 104 us               | 1.01x faster | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| xml_etree_generate               | 40.5 ms   | 40.7 ms              | 1.00x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| xml_etree_iterparse              | 49.7 ms   | 50.4 ms              | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| xml_etree_parse                  | 77.2 ms   | 79.1 ms              | 1.02x slower | Significant (t=-16.14) |
+----------------------------------+-----------+----------------------+--------------+------------------------+
| xml_etree_process                | 29.5 ms   | 29.8 ms              | 1.01x slower | Not significant        |
+----------------------------------+-----------+----------------------+--------------+------------------------+

@blurb-it

vstinner

@cmaloney

@cmaloney cmaloney changed the title gh-139871: Update bytearray to contain PyBytesObject gh-139871: Implement bytearray.take_bytes([n]) to efficiently extract bytes

Oct 15, 2025

@cmaloney

@cmaloney cmaloney changed the title gh-139871: Implement bytearray.take_bytes([n]) to efficiently extract bytes gh-139871: Add bytearray.take_bytes([n]) to efficiently extract bytes

Oct 15, 2025

vstinner

cmaloney

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

cmaloney

maurycy

Co-authored-by: Maurycy Pawłowski-Wieroński <5383+maurycy@users.noreply.github.com>

maurycy

… which is resulting in threading failure
Co-authored-by: Maurycy Pawłowski-Wieroński <5383+maurycy@users.noreply.github.com>

cmaloney

cmaloney

cmaloney

On 32 bit systems with 4GB of ram there may be PY_SSIZE_T_MAX
allocatable and the testt would pass as the allocation would succeed.

Add a + 1 so that it's over the max bytes length and an OverflowError
will be raised by bytes.

@cmaloney

vstinner

Co-authored-by: Petr Viktorin <encukou@gmail.com>

CuriousLearner added a commit to CuriousLearner/cpython that referenced this pull request

Nov 13, 2025

CuriousLearner added a commit to CuriousLearner/cpython that referenced this pull request

Nov 14, 2025

CuriousLearner added a commit to CuriousLearner/cpython that referenced this pull request

Nov 14, 2025

StanFromIreland pushed a commit to StanFromIreland/cpython that referenced this pull request

Dec 6, 2025
…ct `bytes` (pythonGH-140128)

Update `bytearray` to contain a `bytes` and provide a zero-copy path to
"extract" the `bytes`. This allows making several code paths more efficient.

This does not move any codepaths to make use of this new API. The documentation
changes include common code patterns which can be made more efficient with
this API.

---

When just changing `bytearray` to contain `bytes` I ran pyperformance on a
`--with-lto --enable-optimizations --with-static-libpython` build and don't see
any major speedups or slowdowns with this; all seems to be in the noise of
my machine (Generally changes under 5% or benchmarks that don't touch
bytes/bytearray).


Co-authored-by: Victor Stinner <vstinner@python.org>
Co-authored-by: Maurycy Pawłowski-Wieroński <5383+maurycy@users.noreply.github.com>