datetime: cache module lookups (2x faster) #148085
Description
Feature or enhancement
Proposal:
gh-148072 got me looking for more places like this.
It's not that frequent: asyncio, sqlite etc. do it, but it turns out that datetime does not:
https://github.com/python/cpython/blob/dea4083aa95/Modules/_datetimemodule.c#L2081
https://github.com/python/cpython/blob/dea4083aa95/Modules/_datetimemodule.c#L1882
https://github.com/python/cpython/blob/dea4083aa95/Modules/_datetimemodule.c#L2063
Benchmark
I've got a branch ready with a very simple caching in datetime_state:
| Benchmark | main-c50d6cd | datetime-cache-time-module-lookups-a49f862 |
|--------------------|:------------:|:------------------------------------------:|
| datetime.timetuple | 260 ns | 126 ns: 2.07x faster |
| datetime.strftime | 784 ns | 509 ns: 1.54x faster |
| date.timetuple | 258 ns | 124 ns: 2.08x faster |
| Geometric mean | (ref) | 1.88x faster |
Where:
import pyperf, datetime
r = pyperf.Runner()
dt = datetime.datetime(2026, 4, 4, 12, 30, 45)
d = datetime.date(2026, 4, 4)
r.bench_func("datetime.timetuple", dt.timetuple)
r.bench_func("datetime.strftime", dt.strftime, "%Y-%m-%d")
r.bench_func("date.timetuple", d.timetuple)
Where:
2026-04-04T14:17:02.794335000+0200 maurycy@gimel /Users/maurycy/work/cpython-main (main c50d6cd) % ./python.exe -c "import sysconfig; print(sysconfig.get_config_var('CONFIG_ARGS'))"
'--enable-optimizations' '--with-lto'
[127] 2026-04-04T14:17:24.011667000+0200 maurycy@gimel /Users/maurycy/src/github.com/maurycy/cpython (datetime-cache-time-module-lookups a49f862) % ./python.exe -c "import sysconfig; print(sysconfig.get_config_var('CONFIG_ARGS'))"
'--enable-optimizations' '--with-lto'
This is macOS@M4.
Has this already been discussed elsewhere?
This is a minor feature, which does not need previous discussion elsewhere
Links to previous discussion of this feature:
This was already discussed:
However, from what I see, the problem with Py_Finalize() and Py_Initialize() was just a static variable, and since #119810 it's now per interprerter: