gh-116159: argparse: performance improvement parsing large number of options#116162
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…er of options When parsing positional vs optional arguments, the use of min with a list comprehension inside of a loop results in quadratic time based on the number of optional arguments given. When combined with use of prefix based argument files and a large number of optional flags, this can result in extremely slow parsing behavior. This replaces the min call with a simple loop with a short circuit to break at the next optional argument. Example test case that exercises this performance behavior: https://gist.github.com/amyreese/b825bc092210ea7b64287f033dc995d8 The test case parses a list of arguments that contains 30,000 copies of `--flag=something`. Using latest 3.12 or 3.13 from main, this takes roughly 15-16 seconds to parse. With the proposed fix, this only takes 80 milliseconds. Before: ``` $ ~/opt/cpython/bin/python3.13 -VV Python 3.13.0a4+ (heads/main:0656509033, Feb 29 2024, 11:59:43) [Clang 15.0.0 (clang-1500.1.0.2.5)] $ ~/opt/cpython/bin/python3.13 test_many_flags.py parsed args in 15,195,914 µs ``` With fix: ``` $ ~/opt/cpython/bin/python3.13 -VV Python 3.13.0a4+ (heads/argparse-options:968aa13a1d, Feb 29 2024, 13:34:49) [Clang 15.0.0 (clang-1500.1.0.2.5)] $ ~/opt/cpython/bin/python3.13 test_many_flags.py parsed args in 79,787 µs ``` Co-authored-by: Zsolt Dollenstein <zsol.zsol@gmail.com>
erlend-aasland
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…er of options (python#116162) When parsing positional vs optional arguments, the use of min with a list comprehension inside of a loop results in quadratic time based on the number of optional arguments given. When combined with use of prefix based argument files and a large number of optional flags, this can result in extremely slow parsing behavior. This replaces the min call with a simple loop with a short circuit to break at the next optional argument. Co-authored-by: Zsolt Dollenstein <zsol.zsol@gmail.com>
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Summary: Upstream PR: python/cpython#116162 This improves performance when parsing a large number of options from multiple seconds to milliseconds. pikachu_dance Reviewed By: fried Differential Revision: D54553600 fbshipit-source-id: da1ca6d110e701bbd491465c00627f29a08af3c5
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…er of options (python#116162) When parsing positional vs optional arguments, the use of min with a list comprehension inside of a loop results in quadratic time based on the number of optional arguments given. When combined with use of prefix based argument files and a large number of optional flags, this can result in extremely slow parsing behavior. This replaces the min call with a simple loop with a short circuit to break at the next optional argument. Co-authored-by: Zsolt Dollenstein <zsol.zsol@gmail.com>
diegorusso
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Apr 17, 2024
…er of options (python#116162) When parsing positional vs optional arguments, the use of min with a list comprehension inside of a loop results in quadratic time based on the number of optional arguments given. When combined with use of prefix based argument files and a large number of optional flags, this can result in extremely slow parsing behavior. This replaces the min call with a simple loop with a short circuit to break at the next optional argument. Co-authored-by: Zsolt Dollenstein <zsol.zsol@gmail.com>
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When parsing positional vs optional arguments, the use of min with a
list comprehension inside of a loop results in quadratic time based
on the number of optional arguments given. When combined with use of
prefix based argument files and a large number of optional flags, this
can result in extremely slow parsing behavior.
This replaces the min call with a simple loop with a short circuit to
break at the next optional argument.
Example test case that exercises this performance behavior:
https://gist.github.com/amyreese/b825bc092210ea7b64287f033dc995d8
The test case parses a list of arguments that contains 30,000 copies
of
--flag=something. Using latest 3.12 or 3.13 from main, this takesroughly 15-16 seconds to parse. With the proposed fix, this only takes
80 milliseconds.
Before:
With fix:
Co-authored-by: Zsolt Dollenstein zsol.zsol@gmail.com