Skip to content

gh-139476: Optimize range[:] slice #139556

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
wants to merge 2 commits into from
Closed

gh-139476: Optimize range[:] slice #139556

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
2ce37e4
Commit
StanFromIreland Oct 4, 2025
466e293
Commit
StanFromIreland Oct 4, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
11 changes: 11 additions & 0 deletions Lib/test/test_range.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -584,6 +584,17 @@ def check(start, stop, step=None):
check(0, -1)
check(-1, -3, -1)

for test in (range(5), range(0), range(1, 10, 2), range(10, 0, -1), range(-1, 200, 1)):
with self.subTest(test=test):
self.assertIs(test, test[:])
self.assertIs(test, test[:len(test):])
self.assertIs(test, test[0:len(test):1])

if len(test) > 1:
self.assertIsNot(test, test[1:len(test):2])
self.assertIsNot(test, test[1:])
self.assertIsNot(test, test[:-1])

def test_contains(self):
r = range(10)
self.assertIn(0, r)
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2025-10-04-14-06-40.gh-issue-139476.02iIfn.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
:func:`range` slicing with ``[:]`` and ``[:len(r):]`` no longer creates a copy,
it now returns the same object, consistent with :func:`copy.copy`.
7 changes: 7 additions & 0 deletions Objects/rangeobject.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -413,6 +413,13 @@ compute_slice(rangeobject *r, PyObject *_slice)
if (error == -1)
return NULL;

if (start == _PyLong_GetZero()
&& step == _PyLong_GetOne()
&& (slice->stop == Py_None || PyObject_RichCompareBool(stop, r->length, Py_EQ) == 1))
{
return Py_NewRef(r);
}
Comment on lines +416 to +421
Copy link
Member

@picnixz picnixz Oct 5, 2025 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

PyObject_RichCompareBool can raise an error. Handling it would then make the code more complex. So I'm rather against that change as it's not so trivial.

Also, start == _PyLong_GetZero() is not correct because it's not guaranteed that 0 will always be immortal (though it should in general and I see that there is code that is doing this for 1). I actually thought that we had the indices as C integers and not Python ones, but it appears that it's not the case.


substep = PyNumber_Multiply(r->step, step);
if (substep == NULL) goto fail;
Py_CLEAR(step);
Expand Down
Loading