Python中分数的相关使用教程
你可能不需要经常处理分数，但当你需要时，Python的Fraction类会给你很大的帮助。在该指南中，我将提供一些有趣的实例，用于展示如何处理分数，突出显示一些很酷的功能。
1 基础
Fraction类在Lib/fractions.py文件中，所以可以这样导入：
from fractions import Fraction
有很多种实例化Fraction类的方法。
首先，你可以传入分子和分母：
>>> Fraction(1, 2) Fraction(1, 2)
或者利用另一个分数进行实例化：
>>> f = Fraction(1, 2) >>> Fraction(f) Fraction(1, 2)
使用一个浮点数进行实例化：
>>> Fraction(2.5) Fraction(5, 2)
或者使用一个 decimal：
>>> from decimal import Decimal
>>> Fraction(Decimal('1.1'))
Fraction(11, 10)
最后一种方法，可能是最有趣的一种方法，你可以使用一个字符串实例化Fraction类：
>>> Fraction('9/16')
Fraction(9, 16)
本质上讲，Fraction类这么设计，目的就是为了让你在实例化该类之前不需要做很多处理。Fraction类知道如何处理多种不同的数据类型。
2 自动约分
约分并不是很难，但是对于一些复杂的分数，约分还是要费点事的。Fraction类在这方面特别有用，因为它能自动约分分数。
>>> Fraction(153, 272) Fraction(9, 16)
纯粹靠想，你可能无法约分153/172，但是Fraction类能很快地完成约分。
3 二元运算
你可以像对待整数和浮点数一样，在Fraction对象上执行二元运算。
两个分数进行相加操作：
>>> Fraction(1, 2) + Fraction(3, 4) Fraction(5, 4)
这样操作就很方便了，但是你也可以混合整数或浮点数。如你所料，Fraction对象和一个整数进行相加返回一个Fraction对象，但和一个浮点数进行相加返回一个浮点数。
>>> Fraction(5, 16) + 3 Fraction(53, 16) >>> Fraction(5, 16) + 3.0 3.3125
这里有一些其他的二元运算的例子：
>>> Fraction(5, 16) - Fraction(1, 4) Fraction(1, 16) >>> Fraction(1, 16) * Fraction(3, 16) Fraction(3, 256) >>> Fraction(3, 16) / Fraction(1, 8) Fraction(3, 2)
现在让我们试试乘方操作：
>>> Fraction(1, 8) ** Fraction(1, 2) 0.3535533905932738
它返回一个浮点数，可能是因为分数不能进行合理的计算。实际上我们可以使用limit_denominator方法得到一个近似的Fraction值。
>>> f = Fraction(1, 8) ** Fraction(1, 2) >>> Fraction(f).limit_denominator() Fraction(235416, 665857)
记住，你可以混合字符串和其他上边实例化部分中提到的数据类型。
>>> Fraction("1/2") + Fraction(2.0)
Fraction(5, 2)
>>> Fraction(2) * Fraction(" 1/2 ")
Fraction(1, 1)
4 获取Fraction对象的属性
你已经有了一个Fraction对象，并且已经做了一些计算，现在我们如何访问它的属性呢？
不阅读文档的话，你或许会尝试Fraction.numerator和Fraction.denominator，事实证明你是正确的。
>>> f = Fraction(221, 234) + Fraction(1, 2) >>> f.numerator 13 >>> f.denominator 9
或者作为一个字符串，打印整个分数：
>>> print f 13/9 >>> a = str(f) >>> a '13/9'
这不是Fraction类的一部分，它是在fractions库中的。利用它你可以快速找到两个数的最大公约数。
首先导入：
from fractions import gcd
一些例子：
>>> gcd(100, 75) 25 >>> gcd(221, 234) 13
6 总结
希望你已经学到了一些关于在Python中处理分数的东西。如果你想阅读更多内容，可以查看文档。如果你感觉学起来非常有动力，可以看看源代码。
如果你有更有趣的分数使用方法，告诉我，我会将它们添加到指南中。
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