Question

我是一个python /编程newb，我是自学python。不幸的是我真的卡住了！我在第34章＆＃34;如何像计算机科学家一样思考＆＃34;。这里的对象是使用链表编写优先级队列ADT的实现。

我在第22行和第32行收到错误。我对此错误的理解是，我的一个或多个节点对象没有属性＆＃34; cargo＆＃34;。我不明白这一点，因为我的所有节点对象在创建时都被分配了一个＆＃34; None＆＃34;或某个数字。节点对象按照书中的说明编写。

我应该提一下，LINE 31的工作很精细。当我添加LINE 32时，我只会遇到一个问题，它会调用LINE 22（这显然是问题隐藏的地方），我收到错误。

任何见解都会有所帮助。非常感谢你!!!

我以较小的规模重现了这个问题：

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


class Priority_Queue_For_Linked():
def __init__ (self):
    self.max = None
    self.nextmax = None
    self.min = None
    self.length = 0

def insert (self, cargo):
    node = Node(cargo)
    if self.length == 0:
        node = self.max = self.min
        self.length = 1
        return

    if node.cargo > self.max.cargo:     # <--LINE 22
        notmaxanymore = self.max
        notmaxanymore.next = node
        node = self.max
        self.nextmax = notmaxanymore
        self.length += 1
        return

testlist = Priority_Queue_For_Linked()
testlist.insert(12)
testlist.insert(22)                     # <--LINE 32

这是错误：

=== RESTART: /Users/Desktop/Programming Career/Untitled6.py ===

Traceback (most recent call last):
File "/Users/Desktop/Programming Career/Untitled6.py", line 31, in <module>
testlist.insert(22)# <--line 32
  File "/Users/Desktop/Programming Career/Untitled6.py", line 21, in insert
if node.cargo > self.max.cargo:# <--line 22
AttributeError: 'NoneType' object has no attribute 'cargo'

我怀疑你需要更多的上下文，但如果它有帮助，这里是所有的代码：

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

def __str__(self):
    return str(self.cargo)

def print_backward (self):
    if self.next != None:
        tail = self.next
        tail.print_backward()
    print self.cargo,

def print_list(node):
    while node:
        print node,
        node = node.next
    print


class Priority_Queue_For_Linked():
def __init__ (self):
    self.max = None
    self.nextmax = None
    self.min = None
    self.length = 0

def is_empty (self):
    if self.length == 0:
        print "List is empty."

def insert (self, cargo):
    node = Node(cargo)
    if self.length == 0:
        node = self.max = self.min
        self.length = 1
        return

    if node.cargo > self.max.cargo:########40
        notmaxanymore = self.max
        notmaxanymore.next = node
        node = self.max
        self.nextmax = notmaxanymore
        self.length += 1
        return

    if node.cargo < self.min.cargo:
        notminanymore = self.min
        node.next = notminanymore
        node = self.min
        self.length += 1
        return

    else:
        comparisonnode = self.min.next
        comparisonprev = self.min
        for i in range (2, self.length):
            if node.cargo < comparisonnode.cargo:
                node.next = comparisonnode
                comparisonprev.next = node
                self.length += 1
                break
            comparisonnode = comparisonnode.next
            comparisonprev = comparisonprev.next

def remove (self):
    maxtoremove = self.max
    self.max = self.nextmax
    self.max.next = None
    length -=1 
    return maxtoremove.cargo

def print_list(self):
    tempnode = self.min
    print "[",
    while not tempnode == None:
        print tempnode,
        tempnode = tempnode.next
    print "]"



testlist = Priority_Queue_For_Linked()
testlist.insert(12)
testlist.insert(22)#######86

Answer 1

当您插入第一个项目时，您的作业出现问题：

if self.length == 0:
    node = self.max = self.min
    self.length = 1
    return

这不会更改self.max或self.min的值，它们将保持为None，当然不会cargo。self.max = self.min = node您还将丢失要添加的节点。我假设你想这样做：

import random
play = 'y'
Original = 1
while play.lower() == 'y':
    chance = random.randint(0,3)
    if chance == 0:
        print("Unlucky.... better luck next time")
    else:
        newnumber = Original*2
        print (newnumber)  
    play = input("Play again?[y/n]: ")

Answer 2

Priority_Queue_For_Linked类的public class PageClass{ public PageClass(WebDriver driver){ this.driver = driver; } public void testPage() { driver.get("https://www.google.co.uk/"); } } public class MainTest { public static void main(String[] args){ System.setProperty("webdriver.chrome.driver","chromedriver.linux"); WebDriver driver = new ChromeDriver(); PageClass pageClassTest = new PageClass(driver); pageClassTest.testPage(); } }属性在max方法中定义为None，并且在if语句之前未被更改。

我认为您打算在某个时刻指定一个Node作为该属性的值，但您还没有这样做。

Answer 3

您的代码尝试执行self.max.cargo。在__init__中，您将self.max设置为无，并且您永远不会在其他任何位置更改此值，因此self.max为无。如果您希望能够使用self.max，则需要在某个时刻将其设置为实际节点值。

我的对象显然没有属性＆＃39; cargo＆＃39;

3 个答案: