[issue44307] date.today() is 2x slower than datetime.now().date()

[Paul Ganssle]

Paul Ganssle  added the comment:

Yeah, I knew this was slower and it's been on my long list to look at it (tied 
to this is the fact that `datetime.today()` is basically just a slow version of 
`datetime.now()`, in defiance of user expectations).

My inclination is that we shouldn't re-implement `fromtimestamp` in 
`date.today`, but rather call `date_fromtimestamp` in the fast path. I believe 
that incurs the overhead of creating one additional Python object (an integer), 
but if it's a sufficiently significant speedup, we could possibly refactor 
`date_fromtimestamp` to a version that accepts a C integer and a version that 
accepts a Python integer, then call the version accepting a C integer.

I think this won't give any speedup to `datetime.today`, since `datetime.today` 
will still take the slow path. If we care about this, we *may* be able to 
implement `datetime.today` as an alias for `datetime.now(None)`, assuming there 
are no behavioral differences between the two.

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[issue44307] date.today() is 2x slower than datetime.now().date()

[Ruairidh MacLeod]

Change by Ruairidh MacLeod :


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nosy: +rkm

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[issue44307] date.today() is 2x slower than datetime.now().date()

[Dong-hee Na]

Change by Dong-hee Na :


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nosy: +corona10

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[issue44307] date.today() is 2x slower than datetime.now().date()

[Dong-hee Na]

Change by Dong-hee Na :


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nosy: +p-ganssle

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[issue44307] date.today() is 2x slower than datetime.now().date()

[Anthony Sottile]

New submission from Anthony Sottile :

```console
$ python3.10 -m timeit -s 'from datetime import datetime' 
'datetime.now().date()'
50 loops, best of 5: 708 nsec per loop
$ python3.10 -m timeit -s 'from datetime import date' 'date.today()'
20 loops, best of 5: 1.4 usec per loop
```

this surprised me so I dug into it -- it appears a fast path can be added to 
`date.today()` to make it faster than `datetime.date.now()` -- though I'm 
rather unfamiliar with the functions involved here

here is my ~sloppy patch attempting to add a fast path, I would need some 
guidance to improve it and get it accepted:

```diff
$ git diff -w
diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index 8ef2dad37a..7eaa5d1740 100644
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -2875,6 +2875,17 @@ date_fromtimestamp(PyObject *cls, PyObject *obj)
 static PyObject *
 date_today(PyObject *cls, PyObject *dummy)
 {
+/* fast path, don't call fromtimestamp */
+if ((PyTypeObject *)cls == _DateType) {
+struct tm tm;
+time_t t;
+time();
+localtime_r(, );
+return new_date_ex(tm.tm_year + 1900,
+   tm.tm_mon + 1,
+   tm.tm_mday,
+   (PyTypeObject*)cls);
+} else {
 PyObject *time;
 PyObject *result;
 _Py_IDENTIFIER(fromtimestamp);
@@ -2893,6 +2904,7 @@ date_today(PyObject *cls, PyObject *dummy)
 Py_DECREF(time);
 return result;
 }
+}
 
 /*[clinic input]
 @classmethod
```

after this, `date.today()` is faster!

```console
$ ./python -m timeit -s 'from datetime import datetime' 'datetime.now().date()'
50 loops, best of 5: 764 nsec per loop
$ ./python -m timeit -s 'from datetime import date' 'date.today()'
50 loops, best of 5: 407 nsec per loop
```

\o/

--
components: Extension Modules
messages: 395061
nosy: Anthony Sottile
priority: normal
severity: normal
status: open
title: date.today() is 2x slower than datetime.now().date()
type: performance
versions: Python 3.11

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