From b27406c03e662ee33c8d5f48a7478bac93decee8 Mon Sep 17 00:00:00 2001 From: Mark Dickinson Date: Fri, 9 May 2008 13:42:33 +0000 Subject: [PATCH] Issue 2748: fix __ceil__, __floor__ and __round__ magic methods in Decimal, and add tests. --- Lib/decimal.py | 105 +++++++++++++++++++++++++++++++++++---- Lib/test/test_decimal.py | 88 ++++++++++++++++++++++++++++++++ Misc/NEWS | 4 ++ 3 files changed, 188 insertions(+), 9 deletions(-) diff --git a/Lib/decimal.py b/Lib/decimal.py index f008b5a2c27..a61025aaa23 100644 --- a/Lib/decimal.py +++ b/Lib/decimal.py @@ -1645,9 +1645,6 @@ class Decimal(_numbers.Real): else: return -1 - def __round__(self): - return self._round_down(0) - def _round_up(self, prec): """Rounds away from 0.""" return -self._round_down(prec) @@ -1683,9 +1680,6 @@ class Decimal(_numbers.Real): else: return -self._round_down(prec) - def __ceil__(self): - return self._round_ceiling(0) - def _round_floor(self, prec): """Rounds down (not towards 0 if negative)""" if not self._sign: @@ -1693,9 +1687,6 @@ class Decimal(_numbers.Real): else: return -self._round_down(prec) - def __floor__(self): - return self._round_floor(0) - def _round_05up(self, prec): """Round down unless digit prec-1 is 0 or 5.""" if prec and self._int[prec-1] not in '05': @@ -1703,6 +1694,102 @@ class Decimal(_numbers.Real): else: return -self._round_down(prec) + def __round__(self, n=None): + """Round self to the nearest integer, or to a given precision. + + If only one argument is supplied, round a finite Decimal + instance self to the nearest integer. If self is infinite or + a NaN then a Python exception is raised. If self is finite + and lies exactly halfway between two integers then it is + rounded to the integer with even last digit. + + >>> round(Decimal('123.456')) + 123 + >>> round(Decimal('-456.789')) + -457 + >>> round(Decimal('-3.0')) + -3 + >>> round(Decimal('2.5')) + 2 + >>> round(Decimal('3.5')) + 4 + >>> round(Decimal('Inf')) + Traceback (most recent call last): + ... + ... + ... + OverflowError: cannot round an infinity + >>> round(Decimal('NaN')) + Traceback (most recent call last): + ... + ... + ... + ValueError: cannot round a NaN + + If a second argument n is supplied, self is rounded to n + decimal places using the rounding mode for the current + context. + + For an integer n, round(self, -n) is exactly equivalent to + self.quantize(Decimal('1En')). + + >>> round(Decimal('123.456'), 0) + Decimal('123') + >>> round(Decimal('123.456'), 2) + Decimal('123.46') + >>> round(Decimal('123.456'), -2) + Decimal('1E+2') + >>> round(Decimal('-Infinity'), 37) + Decimal('NaN') + >>> round(Decimal('sNaN123'), 0) + Decimal('NaN123') + + """ + if n is not None: + # two-argument form: use the equivalent quantize call + if not isinstance(n, int): + raise TypeError('Second argument to round should be integral') + exp = _dec_from_triple(0, '1', -n) + return self.quantize(exp) + + # one-argument form + if self._is_special: + if self.is_nan(): + raise ValueError("cannot round a NaN") + else: + raise OverflowError("cannot round an infinity") + return int(self._rescale(0, ROUND_HALF_EVEN)) + + def __floor__(self): + """Return the floor of self, as an integer. + + For a finite Decimal instance self, return the greatest + integer n such that n <= self. If self is infinite or a NaN + then a Python exception is raised. + + """ + if self._is_special: + if self.is_nan(): + raise ValueError("cannot round a NaN") + else: + raise OverflowError("cannot round an infinity") + return int(self._rescale(0, ROUND_FLOOR)) + + def __ceil__(self): + """Return the ceiling of self, as an integer. + + For a finite Decimal instance self, return the least integer n + such that n >= self. If self is infinite or a NaN then a + Python exception is raised. + + """ + if self._is_special: + if self.is_nan(): + raise ValueError("cannot round a NaN") + else: + raise OverflowError("cannot round an infinity") + return int(self._rescale(0, ROUND_CEILING)) + def fma(self, other, third, context=None): """Fused multiply-add. diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py index bb27eec3e8d..b4f942ec0bc 100644 --- a/Lib/test/test_decimal.py +++ b/Lib/test/test_decimal.py @@ -1150,6 +1150,94 @@ class DecimalUsabilityTest(unittest.TestCase): self.assertEqual(float(d1), 66) self.assertEqual(float(d2), 15.32) + #floor + test_pairs = [ + ('123.00', 123), + ('3.2', 3), + ('3.54', 3), + ('3.899', 3), + ('-2.3', -3), + ('-11.0', -11), + ('0.0', 0), + ('-0E3', 0), + ] + for d, i in test_pairs: + self.assertEqual(math.floor(Decimal(d)), i) + self.assertRaises(ValueError, math.floor, Decimal('-NaN')) + self.assertRaises(ValueError, math.floor, Decimal('sNaN')) + self.assertRaises(ValueError, math.floor, Decimal('NaN123')) + self.assertRaises(OverflowError, math.floor, Decimal('Inf')) + self.assertRaises(OverflowError, math.floor, Decimal('-Inf')) + + #ceiling + test_pairs = [ + ('123.00', 123), + ('3.2', 4), + ('3.54', 4), + ('3.899', 4), + ('-2.3', -2), + ('-11.0', -11), + ('0.0', 0), + ('-0E3', 0), + ] + for d, i in test_pairs: + self.assertEqual(math.ceil(Decimal(d)), i) + self.assertRaises(ValueError, math.ceil, Decimal('-NaN')) + self.assertRaises(ValueError, math.ceil, Decimal('sNaN')) + self.assertRaises(ValueError, math.ceil, Decimal('NaN123')) + self.assertRaises(OverflowError, math.ceil, Decimal('Inf')) + self.assertRaises(OverflowError, math.ceil, Decimal('-Inf')) + + #round, single argument + test_pairs = [ + ('123.00', 123), + ('3.2', 3), + ('3.54', 4), + ('3.899', 4), + ('-2.3', -2), + ('-11.0', -11), + ('0.0', 0), + ('-0E3', 0), + ('-3.5', -4), + ('-2.5', -2), + ('-1.5', -2), + ('-0.5', 0), + ('0.5', 0), + ('1.5', 2), + ('2.5', 2), + ('3.5', 4), + ] + for d, i in test_pairs: + self.assertEqual(round(Decimal(d)), i) + self.assertRaises(ValueError, round, Decimal('-NaN')) + self.assertRaises(ValueError, round, Decimal('sNaN')) + self.assertRaises(ValueError, round, Decimal('NaN123')) + self.assertRaises(OverflowError, round, Decimal('Inf')) + self.assertRaises(OverflowError, round, Decimal('-Inf')) + + #round, two arguments; this is essentially equivalent + #to quantize, which is already extensively tested + test_triples = [ + ('123.456', -4, '0E+4'), + ('123.456', -3, '0E+3'), + ('123.456', -2, '1E+2'), + ('123.456', -1, '1.2E+2'), + ('123.456', 0, '123'), + ('123.456', 1, '123.5'), + ('123.456', 2, '123.46'), + ('123.456', 3, '123.456'), + ('123.456', 4, '123.4560'), + ('123.455', 2, '123.46'), + ('123.445', 2, '123.44'), + ('Inf', 4, 'NaN'), + ('-Inf', -23, 'NaN'), + ('sNaN314', 3, 'NaN314'), + ] + for d, n, r in test_triples: + self.assertEqual(str(round(Decimal(d), n)), r) + + + def test_eval_round_trip(self): #with zero diff --git a/Misc/NEWS b/Misc/NEWS index aaa6382ee44..32d1b5d3a7c 100644 --- a/Misc/NEWS +++ b/Misc/NEWS @@ -18,6 +18,10 @@ Extension Modules Library ------- +- The Decimal module gained the magic methods __round__, __ceil__, + __floor__ and __trunc__, to give support for round, math.ceil, + math.floor and math.trunc. + - The user module has been removed. - The mutex module has been removed.