python - 在子类中打印 python List

Question

我有一个父类(super class)如下:

class Container(object):
    """ Holds hashable objects. Objects may occur 0 or more times """
    def __init__(self):
        """ Creates a new container with no objects in it. I.e., any object 
            occurs 0 times in self. """
        self.vals = {}
    def insert(self, e):
        """ assumes e is hashable
            Increases the number times e occurs in self by 1. """
        try:
            self.vals[e] += 1
        except:
            self.vals[e] = 1
    def __str__(self):
        s = ""
        for i in sorted(self.vals.keys()):
            if self.vals[i] != 0:
                s += str(i)+":"+str(self.vals[i])+"\n"
        return s

我在一个子类上工作:

class Bag(Container):
    def remove(self, e):
        """ assumes e is hashable
            If e occurs in self, reduces the number of 
            times it occurs in self by 1. Otherwise does nothing. """
        # write code here
        if e in self.vals.keys():
            self.vals[e] -= 1

    def count(self, e):
        """ assumes e is hashable
            Returns the number of times e occurs in self. """
        # write code here
        if e not in self.vals.keys():
            return 0
        else:
            return self.vals[e]

    def __add__(self, other):
        new_dict = other.vals
        for e in self.vals.keys():
            if e in other.vals.keys():
                new_dict[e] += self.vals[e]
            else:
                new_dict[e] = self.vals[e]
        return new_dict

    def __str__(self):
        s1 = ""
        for i in sorted(self.new_dict.keys()):
            s1 += str(i)+":"+str(self.new_dict[i])+"\n"
        return s1

运行测试用例时:

• a = 袋子()
• a.insert(3)
• a.insert(5)
• b = 袋子()
• b.插入(5)
• b.插入(5)
• b.插入(5)
• 打印(a+b)

我的输出是:

{3:1, 5:4}

但是，预期的输出应该是:

3:1

5:4

如何获得正确格式的输出？非常感谢!

Answer 1

因为一旦你添加了 a 和 b 你就不再有一个 Bag，只有一个普通的字典。

>>> type(a)
__main__.Bag
>>> type(b)
__main__.Bag
>>> type(a+b)
dict

如果你想添加 Bags 以返回另一个 Bag，你必须相应地修改你的 __add__ 函数，这样它返回一个 Bag 而不是 new_dict ，这只是一个普通的字典。