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bpo-36781: Optimize sum() for bools. #13074

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Merged
DinoV merged 4 commits into from
Sep 10, 2019
Merged

bpo-36781: Optimize sum() for bools. #13074

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0cd8974
Optimize sum() for bools.
serhiy-storchaka May 3, 2019
cb3c565
Merge branch 'master' into sum-bool
serhiy-storchaka May 6, 2019
887a0a5
Fix sum([], False).
serhiy-storchaka May 6, 2019
cbf307d
Add a NEWS entry.
serhiy-storchaka May 6, 2019
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16 changes: 16 additions & 0 deletions Lib/test/test_builtin.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1299,6 +1299,22 @@ def test_sum(self):

self.assertEqual(sum(range(10), 1000), 1045)
self.assertEqual(sum(range(10), start=1000), 1045)
self.assertEqual(sum(range(10), 2**31-5), 2**31+40)
self.assertEqual(sum(range(10), 2**63-5), 2**63+40)

self.assertEqual(sum(i % 2 != 0 for i in range(10)), 5)
self.assertEqual(sum((i % 2 != 0 for i in range(10)), 2**31-3),
2**31+2)
self.assertEqual(sum((i % 2 != 0 for i in range(10)), 2**63-3),
2**63+2)

self.assertEqual(sum(i / 2 for i in range(10)), 22.5)
self.assertEqual(sum((i / 2 for i in range(10)), 1000), 1022.5)
self.assertEqual(sum((i / 2 for i in range(10)), 1000.25), 1022.75)
self.assertEqual(sum([0.5, 1]), 1.5)
self.assertEqual(sum([1, 0.5]), 1.5)
self.assertEqual(repr(sum([-0.0])), '0.0')
self.assertEqual(repr(sum([-0.0], -0.0)), '-0.0')

self.assertRaises(TypeError, sum)
self.assertRaises(TypeError, sum, 42)
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6 changes: 3 additions & 3 deletions Python/bltinmodule.c
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Expand Up @@ -2357,7 +2357,7 @@ builtin_sum_impl(PyObject *module, PyObject *iterable, PyObject *start)
Assumes all inputs are the same type. If the assumption fails, default
to the more general routine.
*/
if (PyLong_CheckExact(result)) {
if (PyLong_CheckExact(result) || PyBool_Check(result)) {
int overflow;
long i_result = PyLong_AsLongAndOverflow(result, &overflow);
/* If this already overflowed, don't even enter the loop. */
Expand All @@ -2373,7 +2373,7 @@ builtin_sum_impl(PyObject *module, PyObject *iterable, PyObject *start)
return NULL;
return PyLong_FromLong(i_result);
}
if (PyLong_CheckExact(item)) {
if (PyLong_CheckExact(item) || PyBool_Check(item)) {
long b = PyLong_AsLongAndOverflow(item, &overflow);
long x = i_result + b;
if (overflow == 0 && ((x^i_result) >= 0 || (x^b) >= 0)) {
Expand Down Expand Up @@ -2419,7 +2419,7 @@ builtin_sum_impl(PyObject *module, PyObject *iterable, PyObject *start)
Py_DECREF(item);
continue;
}
if (PyLong_CheckExact(item)) {
if (PyLong_Check(item)) {
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@pppery pppery May 5, 2019

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Why is this not PyLong_CheckExact(item) || PyBool_Check(item) like the one above?

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@serhiy-storchaka serhiy-storchaka May 6, 2019

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Because why not? This extends the optimization to other int subclasses.

There is a reason why PyLong_Check(item) is not used above: because __radd__ method in the int subclass takes precedence. But for float+int it is not used.

long value;
int overflow;
value = PyLong_AsLongAndOverflow(item, &overflow);
Expand Down