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Title: bpo-33234 Improve list() pre-sizing for inputs with known lengths (no __length_hint__) by pablogsal · Pull Request #9846 · python/cpython · GitHub

Open Graph Title: bpo-33234 Improve list() pre-sizing for inputs with known lengths (no __length_hint__) by pablogsal · Pull Request #9846 · python/cpython

X Title: bpo-33234 Improve list() pre-sizing for inputs with known lengths (no __length_hint__) by pablogsal · Pull Request #9846 · python/cpython

Description: This is a version of #6493 that only preallocates the list when __len__ is available to reduce memory overallocation and possible performance hit on big iterables. This are the L1 and L2 cache misses and related information: THIS PR ❯ perf stat -r 200 -B -e cache-references,cache-misses,cycles,instructions,branches,faults,migrations ./python -c " for _ in range(1000): list([0]*10000) " Performance counter stats for './python -c for _ in range(1000): list([0]*10000) ' (200 runs): 1,151,365 cache-references:u ( +- 0.47% ) 5,686 cache-misses:u # 0.494 % of all cache refs ( +- 8.06% ) 370,237,437 cycles:u ( +- 0.05% ) 542,049,270 instructions:u # 1.46 insn per cycle ( +- 0.00% ) 134,146,925 branches:u ( +- 0.00% ) 8,031 faults:u ( +- 0.00% ) 0 migrations:u 0.122170 +- 0.000307 seconds time elapsed ( +- 0.25% ) MASTER ❯ perf stat -r 200 -B -e cache-references,cache-misses,cycles,instructions,branches,faults,migrations ./python -c "for _ in range(1000): list([0]*10000) " Performance counter stats for './python -c for _ in range(1000): list([0]*10000) ' (200 runs): 1,275,440 cache-references:u ( +- 0.61% ) 21,895 cache-misses:u # 1.717 % of all cache refs ( +- 4.69% ) 392,293,096 cycles:u ( +- 0.22% ) 543,254,939 instructions:u # 1.38 insn per cycle ( +- 0.00% ) 134,549,173 branches:u ( +- 0.00% ) 10,039 faults:u ( +- 0.00% ) 0 migrations:u 0.133171 +- 0.000463 seconds time elapsed ( +- 0.35% ) https://bugs.python.org/issue33234

Open Graph Description: This is a version of #6493 that only preallocates the list when __len__ is available to reduce memory overallocation and possible performance hit on big iterables. This are the L1 and L2 cache miss...

X Description: This is a version of #6493 that only preallocates the list when __len__ is available to reduce memory overallocation and possible performance hit on big iterables. This are the L1 and L2 cache miss...

Opengraph URL: https://github.com/python/cpython/pull/9846

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bpo-33234 Improve list() pre-sizing for inputs with known lengths (no __length_hint__) https://github.com/python/cpython/pull/9846/files/39a87576b5a3075ec5e0a512065901b436bf8e54#top
Show all changes 10 commits https://github.com/python/cpython/pull/9846/files
7602879 Improve list() pre-sizing for inputs with known lengths pablogsal Apr 17, 2018 https://github.com/python/cpython/pull/9846/commits/76028798d0ddef4e6d88c0313db691592bcdd58a
39a8757 Preallocate only when __len__ is available to avoid loss of performan… pablogsal Oct 13, 2018 https://github.com/python/cpython/pull/9846/commits/39a87576b5a3075ec5e0a512065901b436bf8e54
ab450b3 Fix NEWS entry and correct style pablogsal Oct 15, 2018 https://github.com/python/cpython/pull/9846/commits/ab450b3d5a453f36a4988d83b391a79bfbfa5a61
717ca67 Use _PyObject_HasLen to check if the object has lenght to avoid overhead pablogsal Oct 23, 2018 https://github.com/python/cpython/pull/9846/commits/717ca6732b8a15b24542648bdba56812b5ef6867
b678442 Simplify implementation and don't capture all expections on error pablogsal Oct 23, 2018 https://github.com/python/cpython/pull/9846/commits/b67844271da9a4cb3046820be74bf6e0c7b46927
b40bd62 Add assert and fix formatting pablogsal Oct 25, 2018 https://github.com/python/cpython/pull/9846/commits/b40bd623c5536dd90a4cc8ebbc72fc5ff0889ca3
3837486 Remove uneeded test modification pablogsal Oct 25, 2018 https://github.com/python/cpython/pull/9846/commits/38374862963005541cb0af9b7a9beb2c7a98b467
b6ff7ce Don't preallocate if list is modified when calling PyObject_Size pablogsal Oct 26, 2018 https://github.com/python/cpython/pull/9846/commits/b6ff7ce618bc958a4be4cf29aa98a622cf4cebea
e7f8c46 Improve readability in the error handling branch pablogsal Oct 26, 2018 https://github.com/python/cpython/pull/9846/commits/e7f8c464258acf2e82278909fb5e1a792aa65dbf
0a6c8ba Capture only TypeError as suggested by Serhiy pablogsal Oct 28, 2018 https://github.com/python/cpython/pull/9846/commits/0a6c8ba7d2bc269767e0bdbec283b36f59817d22
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