在Python中将返回的“值”和字符串进行比较

Question

我有一个Python脚本，它会把输入的内容变成一个链表，然后比较里面的字符，以确保所有打开的括号都有正确顺序的闭合括号。

比如说，(9-{5*2(1+1)}) 是对的，返回True；而 (9-{5*2{1+1))) 就不对，返回False。

我遇到的问题是，当我把一个函数的返回值和一个字符串进行比较时，if语句在第152行就停住了。当我中断脚本时，出现了这个错误：

Traceback (most recent call last):
  File "lab2.py", line 195, in <module>
    bracketCheck(list)
  File "lab2.py", line 152, in bracketCheck
    if list.getNodeAtPosition(i) == '(' or list.getNodeAtPosition(i) == '{' or list.getNodeAtPosition(i) == '[':
      File "lab2.py", line 114, in getNodeAtPosition
    currentNode = currentNode.getNext()
KeyboardInterrupt

我的脚本中关于链表的代码，主要是受到DreamInCode的atraub的启发。还有，输入必须一个一个地输入，直到你输入“done”为止：

import sys

stack = []
openbrackets = ['(','{','[']
closebrackets = [')','}',']']

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

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

        def __len__ (self):
            return self.length

        def isEmpty (self):
            if length == 0:
                return True
            else:
                return False 

        def getElement(self):
            print self.__str__()

        def getNext (self):
            return self.next 

        def setElement(self, cargo):
            self.cargo = cargo

        def setNext(self, cargo):
            self.next = cargo

        def hasNext(self):
            return self.next != None

    def __init__(self):
        self.first = LinkedList.Node()
        self.length = 0     

    def __len__ (self):
        return self.length

    def __add__(self, other):
        retList = LinkedList()
        for item in self:
            retList.append(item)
        for item in other:
            retList.append(item)

        return retList

    def getFirst(self):
        return self.first.getNext()

    def currentPoint(self):
        current = self.first.getNext()

    def setFirst(self, cargo):
        toAdd = LinkedList.Node(cargo)
        toAdd.setNext(self.first.getNext())
        self.first.setNext(toAdd)
        self.length += 1

    def removeFirst(self):
        if self.length > 0:
            value = self.first.getNext().getElement()
            self.first.setNext(self.first.getNext().getNext())
            self.length -= 1
            return value
        else:
            print "Error: List is empty"

    def addLast(self, cargo):
        current = self.first

        while current.hasNext():
            current = current.getNext()

        current.setNext(LinkedList.Node(cargo))
        self.length += 1

    def removeLast(self,index=None):
        if index ==None: 
            index = self.length-1

        previous = self.getNodeAtPosition(self.checkIndex(index)-1)
            toRemove = previous.getNext()
            afterNext = None
            if toRemove.hasNext():
                    afterNext = toRemove.getNext()
            previous.setNext(afterNext)
            self.length-=1
            return toRemove.getElement()

    def getLast(self):
        current = self.first

        while current.hasNext():
            current = current.getNext()

        return current

    def moveNext(self):
        current = self.first

    def getNodeAtPosition(self, index):
        currentNode = self.first
        for i in range(index+1):
            currentNode = currentNode.getNext()
        return currentNode

    def __str__ (self):
        if self.length == 0:
            return '[]'

        retString = "["
        currentElement = self.first.getNext()

        for i in range(self.length):
            retString += str(currentElement) + ", "
            currentElement = currentElement.getNext()

        return retString[:-2] + ']'

    def checkIndex(self, index):
        if type(index) != int:
            raise TypeError("Index must be an integer or a slice not a")

        if index < 0:
            index += self.length

        if index >= self.length or index < 0:
            raise IndexError("Index out of bounds")

        return index


def bracketCheck(list):
    checkList = LinkedList()
    opencount=0
    closecount=0

    while(list.first.hasNext):
        isEqual = True
        i=0
        i=i+1
        if list.getNodeAtPosition(i) == '(' or list.getNodeAtPosition(i) == '{' or list.getNodeAtPosition(i) == '[':
            checkList.addLast(list.first.getNodeAtPosition(i))
            opencount = opencount + 1

        if list.getNodeAtPosition(i) == ')':
            closecount = closecount + 1

            if list.first.getLast() == openbrackets[0]:
                checkList.removeLast()
            else:
                isEqual = False

        if list.getNodeAtPosition(i) == '}':
            closecount = closecount + 1

            if list.first.getLast() == openbrackets[1]:
                checkList.removeLast()
            else:
                isEqual = False

        if list.getNodeAtPosition(i) == ']':
            closecount = closecount + 1

            if list.first.getLast() == openbrackets[2]:
                checkList.removeLast()
            else:
                isEqual = False
    '''print checkList'''
    print opencount
    print closecount
    if isEqual == False:
        print "an extra is missing."
    else:
        print "win!"

print "Enter list:"
list = LinkedList()
while input != "done":
    input = raw_input()
    if input == "done":
        break
    list.addLast(input)

print list
bracketCheck(list)

错误处理数据结构条件语句输入验证脚本调试链表括号匹配字符比较

在Python中将返回的“值”和字符串进行比较

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