mirrors/cpython
1
0
Fork 0
mirror of https://github.com/python/cpython.git synced 2025-08-30 21:48:47 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions 7

bpo-45876: Correctly rounded stdev() and pstdev() for the Decimal case (GH-29828)

Browse source
This commit is contained in:
Raymond Hettinger 2021-11-30 18:20:08 -06:00 • committed by GitHub
parent 8a45ca542a
commit a39f46afde
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
2 changed files with 112 additions and 22 deletions
Download patch file Download diff file Expand all files Collapse all files

55
Lib/test/test_statistics.py
View file

@ -2164,9 +2164,9 @@ class TestPStdev(VarianceStdevMixin, NumericTestCase):
class TestSqrtHelpers(unittest.TestCase):
def test_isqrt_frac_rto(self):
def test_integer_sqrt_of_frac_rto(self):
for n, m in itertools.product(range(100), range(1, 1000)):
r = statistics._isqrt_frac_rto(n, m)
r = statistics._integer_sqrt_of_frac_rto(n, m)
self.assertIsInstance(r, int)
if r*r*m == n:
# Root is exact
@ -2177,7 +2177,7 @@ class TestSqrtHelpers(unittest.TestCase):
self.assertTrue(m * (r - 1)**2 < n < m * (r + 1)**2)
@requires_IEEE_754
def test_sqrt_frac(self):
def test_float_sqrt_of_frac(self):
def is_root_correctly_rounded(x: Fraction, root: float) -> bool:
if not x:
@ -2204,22 +2204,59 @@ class TestSqrtHelpers(unittest.TestCase):
denonimator: int = randrange(10 ** randrange(50)) + 1
with self.subTest(numerator=numerator, denonimator=denonimator):
x: Fraction = Fraction(numerator, denonimator)
root: float = statistics._sqrt_frac(numerator, denonimator)
root: float = statistics._float_sqrt_of_frac(numerator, denonimator)
self.assertTrue(is_root_correctly_rounded(x, root))
# Verify that corner cases and error handling match math.sqrt()
self.assertEqual(statistics._sqrt_frac(0, 1), 0.0)
self.assertEqual(statistics._float_sqrt_of_frac(0, 1), 0.0)
with self.assertRaises(ValueError):
statistics._sqrt_frac(-1, 1)
statistics._float_sqrt_of_frac(-1, 1)
with self.assertRaises(ValueError):
statistics._sqrt_frac(1, -1)
statistics._float_sqrt_of_frac(1, -1)
# Error handling for zero denominator matches that for Fraction(1, 0)
with self.assertRaises(ZeroDivisionError):
statistics._sqrt_frac(1, 0)
statistics._float_sqrt_of_frac(1, 0)
# The result is well defined if both inputs are negative
self.assertAlmostEqual(statistics._sqrt_frac(-2, -1), math.sqrt(2.0))
self.assertEqual(statistics._float_sqrt_of_frac(-2, -1), statistics._float_sqrt_of_frac(2, 1))
def test_decimal_sqrt_of_frac(self):
root: Decimal
numerator: int
denominator: int
for root, numerator, denominator in [
(Decimal('0.4481904599041192673635338663'), 200874688349065940678243576378, 1000000000000000000000000000000), # No adj
(Decimal('0.7924949131383786609961759598'), 628048187350206338833590574929, 1000000000000000000000000000000), # Adj up
(Decimal('0.8500554152289934068192208727'), 722594208960136395984391238251, 1000000000000000000000000000000), # Adj down
]:
with decimal.localcontext(decimal.DefaultContext):
self.assertEqual(statistics._decimal_sqrt_of_frac(numerator, denominator), root)
# Confirm expected root with a quad precision decimal computation
with decimal.localcontext(decimal.DefaultContext) as ctx:
ctx.prec *= 4
high_prec_ratio = Decimal(numerator) / Decimal(denominator)
ctx.rounding = decimal.ROUND_05UP
high_prec_root = high_prec_ratio.sqrt()
with decimal.localcontext(decimal.DefaultContext):
target_root = +high_prec_root
self.assertEqual(root, target_root)
# Verify that corner cases and error handling match Decimal.sqrt()
self.assertEqual(statistics._decimal_sqrt_of_frac(0, 1), 0.0)
with self.assertRaises(decimal.InvalidOperation):
statistics._decimal_sqrt_of_frac(-1, 1)
with self.assertRaises(decimal.InvalidOperation):
statistics._decimal_sqrt_of_frac(1, -1)
# Error handling for zero denominator matches that for Fraction(1, 0)
with self.assertRaises(ZeroDivisionError):
statistics._decimal_sqrt_of_frac(1, 0)
# The result is well defined if both inputs are negative
self.assertEqual(statistics._decimal_sqrt_of_frac(-2, -1), statistics._decimal_sqrt_of_frac(2, 1))
class TestStdev(VarianceStdevMixin, NumericTestCase):