diff options
Diffstat (limited to 'Lib/fractions.py')
| -rw-r--r-- | Lib/fractions.py | 62 |
1 files changed, 54 insertions, 8 deletions
diff --git a/Lib/fractions.py b/Lib/fractions.py index 9624c90..fc8a12c 100644 --- a/Lib/fractions.py +++ b/Lib/fractions.py @@ -3,6 +3,7 @@ """Fraction, infinite-precision, real numbers.""" +from decimal import Decimal import math import numbers import operator @@ -41,13 +42,21 @@ _RATIONAL_FORMAT = re.compile(r""" class Fraction(numbers.Rational): """This class implements rational numbers. - Fraction(8, 6) will produce a rational number equivalent to - 4/3. Both arguments must be Integral. The numerator defaults to 0 - and the denominator defaults to 1 so that Fraction(3) == 3 and - Fraction() == 0. + In the two-argument form of the constructor, Fraction(8, 6) will + produce a rational number equivalent to 4/3. Both arguments must + be Rational. The numerator defaults to 0 and the denominator + defaults to 1 so that Fraction(3) == 3 and Fraction() == 0. - Fraction can also be constructed from strings of the form - '[-+]?[0-9]+((/|.)[0-9]+)?', optionally surrounded by spaces. + Fractions can also be constructed from: + + - numeric strings similar to those accepted by the + float constructor (for example, '-2.3' or '1e10') + + - strings of the form '123/456' + + - float and Decimal instances + + - other Rational instances (including integers) """ @@ -57,8 +66,32 @@ class Fraction(numbers.Rational): def __new__(cls, numerator=0, denominator=None): """Constructs a Rational. - Takes a string like '3/2' or '1.5', another Rational, or a - numerator/denominator pair. + Takes a string like '3/2' or '1.5', another Rational instance, a + numerator/denominator pair, or a float. + + Examples + -------- + + >>> Fraction(10, -8) + Fraction(-5, 4) + >>> Fraction(Fraction(1, 7), 5) + Fraction(1, 35) + >>> Fraction(Fraction(1, 7), Fraction(2, 3)) + Fraction(3, 14) + >>> Fraction('314') + Fraction(314, 1) + >>> Fraction('-35/4') + Fraction(-35, 4) + >>> Fraction('3.1415') # conversion from numeric string + Fraction(6283, 2000) + >>> Fraction('-47e-2') # string may include a decimal exponent + Fraction(-47, 100) + >>> Fraction(1.47) # direct construction from float (exact conversion) + Fraction(6620291452234629, 4503599627370496) + >>> Fraction(2.25) + Fraction(9, 4) + >>> Fraction(Decimal('1.47')) + Fraction(147, 100) """ self = super(Fraction, cls).__new__(cls) @@ -69,6 +102,19 @@ class Fraction(numbers.Rational): self._denominator = numerator.denominator return self + elif isinstance(numerator, float): + # Exact conversion from float + value = Fraction.from_float(numerator) + self._numerator = value._numerator + self._denominator = value._denominator + return self + + elif isinstance(numerator, Decimal): + value = Fraction.from_decimal(numerator) + self._numerator = value._numerator + self._denominator = value._denominator + return self + elif isinstance(numerator, str): # Handle construction from strings. m = _RATIONAL_FORMAT.match(numerator) |