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gh-86768: implement os.lseek with SetFilePointer on Windows #133137

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gh-86768: implement os.lseek with SetFilePointer on Windows #133137

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@aisk aisk commented Apr 29, 2025 •
edited by bedevere-app bot
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This change will introduce a performance regression:

import os
import timeit
f = open("a.py")
print(timeit.timeit("os.lseek(f.fileno(), 1, os.SEEK_CUR)", number=100000000, globals=globals()))
f.close()

Before the change:

PS C:\Users\xxxxx\Source\cpython> .\python.bat a.py
Running Release|x64 interpreter...
93.8409629999951

After the change:

PS C:\Users\xxxxx\Source\cpython> .\python.bat a.py
Running Release|x64 interpreter...
123.18093929998577

However I think it's acceptable because we added a check in the implementation and os.lseek usually won't been called too many times in the real world.

@bedevere-app bedevere-app bot mentioned this pull request Apr 29, 2025
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@aisk aisk marked this pull request as draft April 29, 2025 12:04
@aisk aisk marked this pull request as ready for review April 29, 2025 16:01
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