New submission from Paul Ganssle <p.gans...@gmail.com>:
In the addition of the `fromisoformat()` alternate constructor (bpo-15873:
https://github.com/python/cpython/pull/4699), I noted that I was able to get
some significant speedup by special-casing the `datetime` baseclass in the C
code so that it bypasses the Python constructor, by replacing code that looks
like this:
return PyObject_CallFunction(cls, "iii", year, month, day);
With code that looks like this:
PyObject *result;
if ( (PyTypeObject *)cls == & PyDateTime_DateType ) {
result = new_date_ex(year, month, day, (PyTypeObject *)cls);
} else {
result = PyObject_CallFunction(cls, "iii", year, month, day);
}
return result;
(This is for `date`, but the results are even more striking for `datetime`).
In my initial proof of concept implementation of a `new_date_subclass_ex`
method, I've seen (this is not compiled with optimizations on, mind you)
speedups for the other constructors as well:
Old constructor:
================
Class: date
constructor: 940.5ns
date.fromordinal: 1544.8ns
date.fromtimestamp: 1941.9ns
Class: DateSubclass
constructor: 1016.6ns
date.fromordinal: 1760.3ns
date.fromtimestamp: 2295.3ns
With fastpath:
==============
Class: date
constructor: 964.3ns
date.fromordinal: 997.6ns
date.fromtimestamp: 1130.2ns
Class: DateSubclass
constructor: 1086.9ns
date.fromordinal: 1818.5ns
date.fromtimestamp: 2129.9ns
As you can see, this is a fairly significant speedup in the common case with no
cost in the unusual case and no change in behavior. I propose that we switch
over all the C constructors where it makes sense to do so in date, time and
datetime.
I'll have a PR forthcoming soon.
----------
messages: 308907
nosy: belopolsky, p-ganssle
priority: normal
severity: normal
status: open
title: date, time and datetime alternate constructors should take fast
construction path
type: enhancement
versions: Python 3.7, Python 3.8
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue32403>
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