2.6 版新增。
源代码： Lib/fractions.py
The fractions 模块提供有理数算术支持。
Fraction 实例可以构造自一对整数、另一有理数或字符串。
第 1 个版本要求 numerator and denominator 是实例化的 numbers.Rational 并返回新的 Fraction 实例采用值 numerator/denominator 。若 denominator is 0 ，引发 ZeroDivisionError 。第 2 个版本要求 other_fraction 是实例化的 numbers.Rational 并返回 Fraction instance with the same value. The next two versions accept either a float 或 decimal.Decimal instance, and return a Fraction instance with exactly the same value. Note that due to the usual issues with binary floating-point (see 浮点算术：问题和局限性 ), the argument to Fraction(1.1) is not exactly equal to 11/10, and so Fraction(1.1) does not return Fraction(11, 10) as one might expect. (But see the documentation for the limit_denominator() method below.) The last version of the constructor expects a string or unicode instance. The usual form for this instance is:
[sign] numerator ['/' denominator]
其中可选 sign 可以是 + 或 - 且 numerator and denominator (if present) are strings of decimal digits. In addition, any string that represents a finite value and is accepted by the float constructor is also accepted by the Fraction constructor. In either form the input string may also have leading and/or trailing whitespace. Here are some examples:
>>> from fractions import Fraction >>> Fraction(16, -10) Fraction(-8, 5) >>> Fraction(123) Fraction(123, 1) >>> Fraction() Fraction(0, 1) >>> Fraction('3/7') Fraction(3, 7) >>> Fraction(' -3/7 ') Fraction(-3, 7) >>> Fraction('1.414213 \t\n') Fraction(1414213, 1000000) >>> Fraction('-.125') Fraction(-1, 8) >>> Fraction('7e-6') Fraction(7, 1000000) >>> Fraction(2.25) Fraction(9, 4) >>> Fraction(1.1) Fraction(2476979795053773, 2251799813685248) >>> from decimal import Decimal >>> Fraction(Decimal('1.1')) Fraction(11, 10)
The Fraction class inherits from the abstract base class numbers.Rational , and implements all of the methods and operations from that class. Fraction instances are hashable, and should be treated as immutable. In addition, Fraction 拥有下列方法：
2.7 版改变： The Fraction 构造函数现在接受 float and decimal.Decimal 实例。
This class method constructs a Fraction representing the exact value of flt , which must be a float . Beware that Fraction.from_float(0.3) is not the same value as Fraction(3, 10)
注意
From Python 2.7 onwards, you can also construct a Fraction instance directly from a float .
This class method constructs a Fraction representing the exact value of dec , which must be a decimal.Decimal .
注意
From Python 2.7 onwards, you can also construct a Fraction instance directly from a decimal.Decimal 实例。
Finds and returns the closest Fraction to self that has denominator at most max_denominator. This method is useful for finding rational approximations to a given floating-point number:
>>> from fractions import Fraction >>> Fraction('3.1415926535897932').limit_denominator(1000) Fraction(355, 113)
or for recovering a rational number that’s represented as a float:
>>> from math import pi, cos >>> Fraction(cos(pi/3)) Fraction(4503599627370497, 9007199254740992) >>> Fraction(cos(pi/3)).limit_denominator() Fraction(1, 2) >>> Fraction(1.1).limit_denominator() Fraction(11, 10)
返回最大公约数对于整数 a and b 。若 a or b 非 0，那么绝对值 gcd(a, b) 是最大整数同时除 a and b . gcd(a,b) 拥有相同符号如 b if b 非 0，否则，它获取符号自 a . gcd(0, 0) 返回 0 .
另请参阅
