Issue 26002 and 25974
patches by Upendra Kumar and Stefan Krah speed up median by using bisect, and general speedup for Decimals using as_integer_ratio
This commit is contained in:
Steven D'Aprano
parent
ad039f7548
commit
3b06e24352
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@ -105,6 +105,7 @@ import math
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from fractions import Fraction
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from decimal import Decimal
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from itertools import groupby
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from bisect import bisect_left, bisect_right
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@ -223,56 +224,26 @@ def _exact_ratio(x):
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# Optimise the common case of floats. We expect that the most often
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# used numeric type will be builtin floats, so try to make this as
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# fast as possible.
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if type(x) is float:
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if type(x) is float or type(x) is Decimal:
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return x.as_integer_ratio()
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try:
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# x may be an int, Fraction, or Integral ABC.
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return (x.numerator, x.denominator)
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except AttributeError:
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try:
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# x may be a float subclass.
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# x may be a float or Decimal subclass.
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return x.as_integer_ratio()
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except AttributeError:
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try:
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# x may be a Decimal.
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return _decimal_to_ratio(x)
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except AttributeError:
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# Just give up?
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pass
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# Just give up?
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pass
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except (OverflowError, ValueError):
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# float NAN or INF.
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assert not math.isfinite(x)
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assert not _isfinite(x)
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return (x, None)
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msg = "can't convert type '{}' to numerator/denominator"
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raise TypeError(msg.format(type(x).__name__))
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# FIXME This is faster than Fraction.from_decimal, but still too slow.
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def _decimal_to_ratio(d):
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"""Convert Decimal d to exact integer ratio (numerator, denominator).
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>>> from decimal import Decimal
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>>> _decimal_to_ratio(Decimal("2.6"))
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(26, 10)
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"""
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sign, digits, exp = d.as_tuple()
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if exp in ('F', 'n', 'N'): # INF, NAN, sNAN
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assert not d.is_finite()
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return (d, None)
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num = 0
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for digit in digits:
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num = num*10 + digit
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if exp < 0:
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den = 10**-exp
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else:
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num *= 10**exp
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den = 1
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if sign:
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num = -num
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return (num, den)
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def _convert(value, T):
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"""Convert value to given numeric type T."""
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if type(value) is T:
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@ -305,6 +276,21 @@ def _counts(data):
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return table
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def _find_lteq(a, x):
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'Locate the leftmost value exactly equal to x'
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i = bisect_left(a, x)
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if i != len(a) and a[i] == x:
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return i
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raise ValueError
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def _find_rteq(a, l, x):
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'Locate the rightmost value exactly equal to x'
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i = bisect_right(a, x, lo=l)
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if i != (len(a)+1) and a[i-1] == x:
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return i-1
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raise ValueError
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# === Measures of central tendency (averages) ===
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def mean(data):
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@ -442,9 +428,15 @@ def median_grouped(data, interval=1):
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except TypeError:
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# Mixed type. For now we just coerce to float.
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L = float(x) - float(interval)/2
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cf = data.index(x) # Number of values below the median interval.
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# FIXME The following line could be more efficient for big lists.
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f = data.count(x) # Number of data points in the median interval.
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# Uses bisection search to search for x in data with log(n) time complexity
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# Find the position of leftmost occurence of x in data
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l1 = _find_lteq(data, x)
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# Find the position of rightmost occurence of x in data[l1...len(data)]
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# Assuming always l1 <= l2
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l2 = _find_rteq(data, l1, x)
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cf = l1
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f = l2 - l1 + 1
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return L + interval*(n/2 - cf)/f
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@ -699,13 +699,12 @@ class ExactRatioTest(unittest.TestCase):
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num, den = statistics._exact_ratio(x)
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self.assertEqual(x, num/den)
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@unittest.skipIf(True, "temporarily disabled: see #25928")
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def test_decimal(self):
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D = Decimal
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_exact_ratio = statistics._exact_ratio
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self.assertEqual(_exact_ratio(D("0.125")), (125, 1000))
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self.assertEqual(_exact_ratio(D("12.345")), (12345, 1000))
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self.assertEqual(_exact_ratio(D("-1.98")), (-198, 100))
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self.assertEqual(_exact_ratio(D("0.125")), (1, 8))
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self.assertEqual(_exact_ratio(D("12.345")), (2469, 200))
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self.assertEqual(_exact_ratio(D("-1.98")), (-99, 50))
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def test_inf(self):
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INF = float("INF")
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@ -731,7 +730,6 @@ class ExactRatioTest(unittest.TestCase):
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self.assertIs(ratio[1], None)
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self.assertEqual(type(ratio[0]), type(nan))
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@unittest.skipIf(True, "temporarily disabled: see #25928")
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def test_decimal_nan(self):
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NAN = Decimal("NAN")
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sNAN = Decimal("sNAN")
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@ -745,18 +743,18 @@ class ExactRatioTest(unittest.TestCase):
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class DecimalToRatioTest(unittest.TestCase):
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# Test _decimal_to_ratio private function.
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# Test _exact_ratio private function.
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def test_infinity(self):
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# Test that INFs are handled correctly.
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inf = Decimal('INF')
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self.assertEqual(statistics._decimal_to_ratio(inf), (inf, None))
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self.assertEqual(statistics._decimal_to_ratio(-inf), (-inf, None))
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self.assertEqual(statistics._exact_ratio(inf), (inf, None))
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self.assertEqual(statistics._exact_ratio(-inf), (-inf, None))
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def test_nan(self):
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# Test that NANs are handled correctly.
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for nan in (Decimal('NAN'), Decimal('sNAN')):
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num, den = statistics._decimal_to_ratio(nan)
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num, den = statistics._exact_ratio(nan)
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# Because NANs always compare non-equal, we cannot use assertEqual.
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# Nor can we use an identity test, as we don't guarantee anything
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# about the object identity.
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@ -769,30 +767,30 @@ class DecimalToRatioTest(unittest.TestCase):
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for d in numbers:
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# First test positive decimals.
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assert d > 0
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num, den = statistics._decimal_to_ratio(d)
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num, den = statistics._exact_ratio(d)
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self.assertGreaterEqual(num, 0)
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self.assertGreater(den, 0)
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# Then test negative decimals.
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num, den = statistics._decimal_to_ratio(-d)
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num, den = statistics._exact_ratio(-d)
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self.assertLessEqual(num, 0)
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self.assertGreater(den, 0)
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def test_negative_exponent(self):
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# Test result when the exponent is negative.
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t = statistics._decimal_to_ratio(Decimal("0.1234"))
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self.assertEqual(t, (1234, 10000))
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t = statistics._exact_ratio(Decimal("0.1234"))
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self.assertEqual(t, (617, 5000))
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def test_positive_exponent(self):
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# Test results when the exponent is positive.
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t = statistics._decimal_to_ratio(Decimal("1.234e7"))
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t = statistics._exact_ratio(Decimal("1.234e7"))
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self.assertEqual(t, (12340000, 1))
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def test_regression_20536(self):
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# Regression test for issue 20536.
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# See http://bugs.python.org/issue20536
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t = statistics._decimal_to_ratio(Decimal("1e2"))
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t = statistics._exact_ratio(Decimal("1e2"))
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self.assertEqual(t, (100, 1))
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t = statistics._decimal_to_ratio(Decimal("1.47e5"))
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t = statistics._exact_ratio(Decimal("1.47e5"))
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self.assertEqual(t, (147000, 1))
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@ -1260,7 +1258,6 @@ class SumSpecialValues(NumericTestCase):
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with decimal.localcontext(decimal.BasicContext):
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self.assertRaises(decimal.InvalidOperation, statistics._sum, data)
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@unittest.skipIf(True, "temporarily disabled: see #25928")
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def test_decimal_snan_raises(self):
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# Adding sNAN should raise InvalidOperation.
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sNAN = Decimal('sNAN')
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