Python如何向类传递多个参数而不强制要求

Question

好的，我刚开始学Python，现在在旧金山的一个社区中心上免费的课程，所以这算是“作业”，但不是学校的作业，所以请详细解释一下。

我们正在学习运算符重载，但我有一个关于类中参数的问题让我很困惑。我可能完全想错了，所以任何帮助都非常感谢。

这是我目前写的类的代码：

class CoinPurse(object):

    def __init__(self, quarters=0, dimes=0, nickels=0, pennies=0):
        self.purse ={'quarters': 0, 'dimes': 0, 'nickels': 0, 'pennies': 0}

    def __setitem__(self, quarters, dimes, nickels, pennies):
        self.purse ={'quarters': quarters, 'dimes': dimes, 'nickels': nickels, 'pennies': pennies}

    def amount(self):
        """ Return the amount of money as a floating point value """
        self.purseamount = 0
        self.purseamount = self.purseamount + ((self.purse['quarters']) * 25)
        self.purseamount = self.purseamount + ((self.purse['dimes']) * 10)
        self.purseamount = self.purseamount + ((self.purse['nickels']) * 5)
        self.purseamount = self.purseamount + self.purse['pennies']
        self.purseamount = float(self.purseamount) / 100

        return float(self.purseamount)

    def quarters(self):
        """ Returns the number of quarters as an integer """

        return int(self.purse['quarters'])

    def dimes(self):
        """ Returns the number of quarters as an integer """

        return int(self.purse['dimes'])

    def nickels(self):
         """ Returns the number of quarters as an integer """

        return int(self.purse['nickels'])

    def pennies(self):
        """ Returns the number of quarters as an integer """

        return int(self.purse['pennies'])

好的，这里是一个测试，用来使用这个类。以后我还需要做很多其他的事情，但现在我只想确保基本功能正常。

x = CoinPurse(quarters=5, pennies=100)
print x.amount()
print x.quarters()
print x.pennies()

我的问题是，我知道我没有正确使用setitem，我该如何传递参数（quarters=5, pennies=100），以便它们可以被添加到字典对象中。我需要同时传递键和值（quarters是键，5是值）……我对此感到迷茫，直到弄清楚这个问题我都无法继续。

顺便说一下，我不能改变x = CoinPurse(quarters=5, pennies=100)，这个写法必须保持不变。

**根据建议编辑后的代码：

class CoinPurse(object):

    def __init__(self, **kwargs):
        self.pquarters = kwargs.get('quarters', 0)
        self.pdimes = kwargs.get('dimes', 0)
        self.pnickels = kwargs.get('nickels', 0)
        self.ppennies = kwargs.get('pennies', 0)


    def amount(self):
        """ Return the amount of money as a floating point value """
        self.purseamount = 0
        self.purseamount = self.purseamount + (self.pquarters * 25)
        self.purseamount = self.purseamount + (self.pdimes * 10)
        self.purseamount = self.purseamount + (self.pnickels * 5)
        self.purseamount = self.purseamount + self.ppennies
        self.purseamount = float(self.purseamount) / 100

        return float(self.purseamount)

    def quarters(self):
        """ Returns the number of quarters as an integer """

        return int(self.pquarters)

    def dimes(self):
        """ Returns the number of quarters as an integer """

        return int(self.pdimes)

    def nickels(self):
        """ Returns the number of quarters as an integer """

        return int(self.pnickels)

    def pennies(self):
        """ Returns the number of quarters as an integer """

        return int(self.ppennies)

Answer 1

如果你把所有的参数都设成关键字，那就简单多了。这样的话，如果没有提供某个硬币的数量，你可以给它设置一个默认值：

def __init__(self, **kwargs):
    quarters = kwargs.get('quarters', 0)
    # etc. for other coins

你还应该检查一下，确保没有其他不允许的关键字被使用。