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.

 New changeset 9f1b7b93f5f0ef589e7b272e127cacf4ce5d23f1 by Alexander Belopolsky (Paul Ganssle) in branch 'master': bpo-32403: Faster date and datetime constructors (#4993) https://github.com/python/cpython/commit/9f1b7b93f5f0ef589e7b272e127cacf4ce5d23f1 

 New changeset 5bd04f964b4f1bcdbd0fa36de04f087c2db07cfe by Alexander Belopolsky (Paul Ganssle) in branch 'master': bpo-10381, bpo-32403: What's new entries for changes to datetime (gh-5814) https://github.com/python/cpython/commit/5bd04f964b4f1bcdbd0fa36de04f087c2db07cfe 

 New changeset fff596f792a0752b0e571fa57809e5752aba6353 by Alexander Belopolsky (Miss Islington (bot)) in branch '3.7': bpo-10381, bpo-32403: What's new entries for changes to datetime (gh-5814) (gh-5929) https://github.com/python/cpython/commit/fff596f792a0752b0e571fa57809e5752aba6353