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gh-109653: Fix py312 regression in the import time of `random` by AlexWaygood · Pull Request #110221 · python/cpython · GitHub

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gh-109653: Fix py312 regression in the import time of random #110221

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Merged
AlexWaygood merged 2 commits into from
Oct 2, 2023
+3 −1
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gh-109653: Fix py312 regression in the import time of random #110221

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a9e3194
Reduce the import time of `random` by 60%
AlexWaygood Oct 2, 2023
e39e4dd
Update Misc/NEWS.d/next/Library/2023-10-02-15-40-10.gh-issue-109653.i…
AlexWaygood Oct 2, 2023
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2 changes: 1 addition & 1 deletion Lib/random.py
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Expand Up @@ -65,7 +65,7 @@

try:
# hashlib is pretty heavy to load, try lean internal module first

gpshead Oct 3, 2023

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

This code is technically awkward... It tried to speed up import time and did so by circumventing hashlib which means that it is loading and using the slowest possible sha512 implementation by default (hashlib will pick up openssl 3's accelerated sha512 support by default on most platforms and not use our builtin). so faster startup time for a slower runtime computation? thankfully this is only ever used by seed() which is a single/constant number of calls for most programs on tiny data so there is zero reason to care about sha512 performance for its purposes. The slower implementation may still be faster on small seed data anyways due to less setup overhead.

Nothing to do here. This works for random's purposes & thanks for the fixup. But this being a regression in the first place demonstrates how fragile direct use of internal details can be. (and indirectly how much in need of an overhaul hashlib.py could use)

I'd file an issue rather than leaving this comment in the merged PR void if there were anything concrete to describe and tackle, there isn't. :)
from _sha512 import sha512 as _sha512
from _sha2 import sha512 as _sha512
except ImportError:
# fallback to official implementation
from hashlib import sha512 as _sha512
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2023-10-02-15-40-10.gh-issue-109653.iB0peK.rst
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@@ -0,0 +1,2 @@
Fix a Python 3.12 regression in the import time of :mod:`random`. Patch by Alex
Waygood.
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