Question

我已经像这样通过循环链接列表定义。

20014860486000000000000000008880

我将项目插入我的列表

20014860486000000000000000019980

我希望有一个循环列表的字符串表示，但看起来class Link(object): def __init__ (self, data, next = None): self.data = data self.next = next class CircularList(object): def __init__ ( self ): self.first = Link(None, None) self.first.next = self.first def insert_first ( self, item ): new_link = Link(item) new_link.next = self.first self.first = new_link def __iter__(self): current = self.first first = current while current.next != first: yield current current = current.next def __str__(self): return str([Link.data for Link in self]) def __repr__(self): return self.__str__()无限循环。我可以正确定义我的迭代器，并获得正确的字符串表示吗？

Answer 1

我打破了台阶。

首先，我将Link重命名为Node。

class Node(object):
    def __init__(self, data, next=None):
        self.data = data
        self.next = next

链接与节点不同 - 节点是保存数据的地方，链接将两个节点连接在一起。

接下来，CircularList类需要进行一些更改。

__init__需要初始化空列表。这意味着根本没有节点。为方便起见，我将self.last定义为大大简化代码（注意，极大，否则你会有更难的事情）。

class CircularList(object):
    def __init__(self):
        self.first = self.last = None

对于insert_first，当列表为空时，您需要处理一个极端情况，以及一般情况。相应地更新self.first和self.last。

def insert_first(self, item):
    if self.first is None:
        self.first = self.last = Node(item)
        self.first.next = self.first
    else:
        self.first = Node(item, self.first)
        self.last.next = self.first

您的__iter__方法也应该以实物回复。评论内联。

def __iter__(self):
    # corner case - yield empty list
    if not self.first:
        yield []
    else:
        # start by yielding the head node
        yield self.first
        cur = self.first.next
        # iterate as long as you do not see the head node again 
        while cur is not self.first:
            yield cur
            cur = cur.next

其他方法保持不变。测试代码：

a = CircularList()
for i in [5, 4, 3, 2, 1]:
    a.insert_first(i)

print(a)
[1, 2, 3, 4, 5]

完整的代码清单

class Node(object):
    def __init__(self, data, next=None):
        self.data = data
        self.next = next

class CircularList(object):
    def __init__(self):
        self.first = self.last = None

    def insert_first(self, item):
        if self.first is None:
            self.first = self.last = Node(item)
            self.first.next = self.first    
        else:
            self.first = Node(item, self.first)
            self.last.next = self.first

    def __iter__(self):
        if not self.first:
            yield []
        else:
            yield self.first
            cur = self.first.next
            while cur is not self.first:
                yield cur
                cur = cur.next

    def __str__(self):
        return str([Link.data for Link in self])

    def __repr__(self):
        return self.__str__()

循环链表代码进入无限循环

1 个答案: