如何修复 __iter__ 方法

Question

from collections import defaultdict
from goody import type_as_str

class Bag:
    def __init__(self, i=None):
        self.bag = []
        if i == None:
            pass  # i is None, do nothing after create empty bag
        elif type(i)==list:
            self.bag.extend(i) # append whole list i into bag with extend method
        else:
            self.bag.append(i) # append single item i into bag 

    def __repr__(self):
        for s in self.bag :
            return s

    def __str__(self):
        for s in self.bag :
            return s

    def __len__ (self):
        if 'Bag()' in self.bag:
            return 0
        else:
            return len(self.bag)
    def unique(self):
        l = []
        if len(self.bag) == 0:
            return 0
        else:
            for x in self.bag:
                if x not in l:
                    l.append(x)
                else:
                    continue
            return len(l)

    def __contains__ (self,i):
        if i in self.bag:
            return True
        else:
            return False

    def count(self,i):
        return self.bag.count(i)

    def add(self,i):
        self.bag.append(i)

    def __add__(self,i):
        for x in i:
           self.bag.append(x)

    def remove(self,i):
        if i not in self.bag:
            raise ValueError
        for x in self.bag:
            if x == i:
                self.bag.remove(x)
                break


    def __eq__ (self,i):
        return self.bag == i 

    def __ne__ (self,i):
        return self.bag != i

    def __iter__(self):
        class PH_iter:
            def __init__(self,i):

                self.l = i

            def add(self,i):
                self.l.append(i)

            def remove(self,i):
                self.l.pop(i)

        return PH_iter(self.l)




if __name__ == '__main__':
#driver tests
import driver
driver.default_file_name = 'bsc1.txt'
#     driver.default_show_exception= True
#     driver.default_show_exception_message= True
#     driver.default_show_traceback= True
driver.driver()

Bag 函数一般返回一个列表。 编写 Bag() 构造一个空包。 写作 Bag(['d','a','b','d','c','b','d']) 用一个 'a'、两个 'b's、一个 'c' 构造一个包，和三个'd'。

应该在 bag 类中定义iter方法以从列表中添加或删除项目。

输入是：

# Test iterator
e-->[i for i in sorted(b)]-->['a', 'b', 'b', 'c', 'd', 'd', 'd']
c-->i = iter(b)
c-->b.add('d')
c-->b.remove('a')
e-->[i for i in sorted(b)]-->['b', 'b', 'c', 'd', 'd', 'd', 'd']
e-->[i for i in sorted(x for x in i)]-->['a', 'b', 'b', 'c', 'd', 'd', 'd']

我得到的错误是：

 94 # Test iterator
 95 *Error: [i for i in sorted(b)] raised exception AttributeError: 'Bag' object has no attribute 'l'
 96 *Error: i = iter(b) raised exception AttributeError: 'Bag' object has no attribute 'l'
 99 *Error: [i for i in sorted(b)] raised exception AttributeError: 'Bag' object has no attribute 'l'
 100 *Error: [i for i in sorted(x for x in i)] raised exception NameError: name 'i' is not defined

谁能帮我修复iter函数以使其正常工作？ 非常感谢。

Answer 1

在__iter__ ，这一行导致了运行时错误

return PH_iter(self.l)

它应该是

return PH_iter(self.bag)

而且这个实现会在迭代之后给你一些惊喜，因为它实际上修改了self.bag的数据内容

您可以通过以下方式改进它

def __iter__(self):
    class PH_iter:
        def __init__(self,i):
            self.l = list(i)  # make a copy of the list i