Python 3.x 使用字符串dunder显示下面的输出？

我试图显示支出列表中属于同一类别的所有项目，然后是每个类别的总额，最后是总总额。例如：

$12.00 Mon, 12 Aug 2019 Food
$15.25 Mon, 12 Aug 2019 Food
Total for Food = $27.25
$8.40 Wed, 14 Aug 2019 Drinks
Total for Drinks = $8.40
$33.00 Tue, 13 Aug 2019 Entertainment
Total for Entertainment = $33.00
Overall Total = $178.55

这是到目前为止我的代码。我想做的是把分类中的所有项目都放到一本字典里，里面有所有的细节，另外一本字典里只有数量，这样我就可以总结了

class ExpenditureList:
    _types = ['Food','Entertainment', 'Drinks']
    def __init__(self):
        self._expenditures = []

    @classmethod
    def ExpenditureTypes(cls):
        return cls._types

    def __str__(self):
        exp = {}
        amount = {}
        temp = None
        for types in ExpenditureList._types:
            exp[types] = []
            amount[types] = []
        for item in self._expenditures:
            if item._type == ExpenditureList._types[0]:
                exp[item._type].append(item)
                amount[item._type].append(item._amount)
            elif item._type == ExpenditureList._types[1]:
                exp[item._type].append(item)
                amount[item._type].append(item._amount)
            elif item._type == ExpenditureList._types[2]:
                exp[item._type].append(item)
                amount[item._type].append(item._amount)

这就是我所做的，我不确定如何返回以获得上述输出