时间戳

首页 > 解决方案 > 类函数在 Python 中找不到位置参数自身

python - 类函数在 Python 中找不到位置参数自身

问题描述

我在 Python 中创建了一个链表类，当调用我定义的 size 函数时，我收到以下错误：

TypeError: get_next() missing 1 required positional argument: 'self'

我尝试调用我定义的另一个函数，该函数也使用该get_next()函数并且它没有产生错误。下面是类定义以及测试代码。

LinkedLists.py：

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

    def get_data(self):
        return self.data

    def get_next(self):
        return self.next_node

    def set_next(self, new_next):
        self.next_node = new_next

class LinkedList(object):
    def __init__(self, head = Node):
        self.head = head

    def insert(self, data):
        new_node = Node(data)

        new_node.set_next(self.head)
        self.head = new_node

    def size(self):
        current = self.head
        count = 0

        while current:
            count += 1
            current = current.get_next()

        return count

    def search(self, data):
        current = self.head
        found = False

        while current:
            if current.get_data() == data:
                found = True
            else:
                current = current.get_next()

        if current is None:
            raise ValueError("Data not in list")

        return current

    def delete(self, data):
        current = self.head
        previous = None
        found = False

        while current and found is False:
            if current.get_data() == data:
                found = True
            else:
                previous = current
                current = current.get_next()

        if current is None:
            raise ValueError("Data not in list")

        if previous is None:
            self.head = current.get_next()
        else:
            previous.set_next(current.get_next())

    def insert_at(self, data, location):
        new_node = Node(data)
        current = self.head
        found = False

        while current and found is False:
            if current.get_data() == data:
                found = True
            else:
                current = current.get_next()

            if current is None:
                raise ValueError("Data not in list")

            new_node.set_next(current.get_next())

            current.set_next(new_node)

LinkedListsTest.py：

from LinkedLists import *

List = LinkedList()

List.insert(5)
List.insert(6)
List.insert(8)
List.delete(6)

print(List.size())

错误的完整追溯：

Traceback (most recent call last):
  File "LinkedListsTest.py", line 10, in <module>
    print(List.size())
  File ".../LinkedLists.py", line 31, in size
    current = current.get_next()
TypeError: get_next() missing 1 required positional argument: 'self'

标签： pythonclasslinked-list

解决方案

您设置self.head为Node class，而不是实例：

def __init__(self, head = Node):
    self.head = head

注意Node那里的参考。Node.get_next()调用未绑定的方法，没有self传入。

但是，不要设置head=Node()为默认值；默认值在函数定义时设置一次，可变的默认值会导致您出现问题，因为您的LinkedList类的所有实例都将共享一个实例。请参阅“Least Astonishment”和可变默认参数。

使用类似的哨兵None来检测您是否需要创建默认值：

def __init__(self, head=None):
    if head is None:
        # create an empty default
        head = Node()
    self.head = head

通过此更正，您的测试打印3.

推荐阅读