cookbook 6.1 温标的转换

任务：

在开氏温度（Kelvin）、摄氏度（Celsius）、华氏温度（Fahrenheit）、兰金温度（Rankine）之间做转换

解决方案：

#coding=utf-8
class Temperature(object):
    coefficients={'c':(1.0,0.0,-273.15),'f':(1.8,-273.15,32.0),'r':(1.8,0.0,0.0)}

    def __init__(self,**kwargs):
        try:
            name,value = kwargs.popitem()
        except KeyError:
            name,value = 'k',0
        if kwargs or name not in 'kcfr':
            kwargs[name] = value
            raise TypeError,'invalid arguments %r' % kwargs
        setattr(self,name,float(value))

    def __getattr__(self,name):
        try:
            eq = self.coefficients[name]
        except KeyError:
            raise AttributeError,name
        return (self.k + eq[1]) + eq[0] + eq[2]
    def __setattr__(self,name,value):
        if name in self.coefficients:
            eq = self.coefficients[name]
            self.k = (value - eq[2]) / eq[0] - eq[1]
        elif name == 'k':
            object.__setattr__(self,name,value)
        else:
            raise AttributeError,name
    def __str__(self):
        return "%s K" % self.k
    def __repr__(self):
        return "Temperature(k=%r)" % self.k

#测试
te = Temperature(f=70)
print te.c