Python - 未定义全局变量（但它是）

Question

所以我正在处理将 CSV 转换为 JSON 的文件，但是我不断收到此错误消息，但似乎无法弄清楚。缩进似乎是正确的，所以我有点迷失在哪里去。代码如下：

回溯（最近一次通话最后）：

  File "/home/uwp/widgets/contentFreshness/freshmap.py", line 308, in <module>
    main()
  File "/home/uwp/widgets/contentFreshness/freshmap.py", line 303, in main
    mySite.writeJSONFile(options)
  File "/home/uwp/widgets/contentFreshness/freshmap.py", line 247, in writeJSONFile
    outputFile.write('"' + str(dateOfCrawl) + '"' )
NameError: global name 'dateOfCrawl' is not defined

代码

class Site:

    dateOfCrawl = 0;

    def __init__(self,csvFilePath):
        self.pageList = [] # ordered list of page IDs
        self.pageData={} # dictionary of individual page dictionaries, indexed on page ID
        self.titleDict = { } # dictionary of unique titles
        self.buildPageData(csvFilePath)
        self.homePageId=self.pageList[0] # only use of site.pageList
        self.depth=0

    def buildPageData(self,csvFilePath):
        global dateOfCrawl
        # read data from CSV file, build a dictionary of page data, including list of children, in order
        lines = csv.reader(open(csvFilePath, "rb"))
        for line in lines:
            pageURL=line[0]
            pageURL=re.sub('\/\Z', '',pageURL) # remove any trailing slash
            self.pageData[pageURL]={}
            self.pageData[pageURL]["URL"]=pageURL
            self.pageData[pageURL]["Title"]=self.cleanTitle(line[1],pageURL)

            # when taking the home page and chop its url the parent will be http:/
            # which should be avoided by setting it to ''
            parent = chopPath(pageURL)
            if(parent == 'http:/'):
                parent=''
                dateOfCrawl = line[2]
            self.pageData[pageURL]["Parent"]= parent
            self.pageData[pageURL]["Modified"]=line[2]
            self.pageData[pageURL]["Children"]=[] 

        list = self.pageData.keys()

        # sort IDs before attempting to match children
        self.pageList = self.pageData.keys()
        self.pageList.sort()

        lineCount = 0       
        for pageURL in self.pageList:
            # record page as child of its parent (parents must already be in the list!)
            parentURL=self.pageData[pageURL]["Parent"]

            if (lineCount > 0):
                while( self.pageData.has_key(parentURL)== False):
                    if(parentURL == ''):
                        sys.exit(pageURL + " has no parent at " + parentURL)
                    parentURL = chopPath(parentURL)
                self.pageData[parentURL]["Children"].append(pageURL)

            lineCount+=1
        self.pageCount=lineCount

    def writeJSONFile(self,options):
        global dateOfCrawl
        outputFile = options ["outputFile"]
        #see http://code.google.com/intl/en/apis/visualization/documentation/reference.html#DataTable
        outputFile.write('[')
        outputFile.write('"' + str(dateOfCrawl) + '"' )
        self.homePage.toJSON(options)
        outputFile.write(']')
        outputFile.close()

Answer 1

您需要定义global dateOfCrawl。将dateOfCrawl = 0; 移动到Site 类的__init__ 中，变成这样：

class Site:
    def __init__(self,csvFilePath):
        global dateOfCrawl
        dateOfCrawl = 0
        ....

Answer 2

您将dateOfCrawl = 0;（请阅读PEP-8）指定为类属性。出于某种原因，您还混入了一个完全独立的global。目前还不清楚为什么dateOfCrawl 应该是一个类（而不是实例）属性，或者为什么你也有global。您可能应该：

1. 使其成为实例属性（将dateOfCrawl = 0 移动到__init__ 中）；那么
2. 在其他方法中访问 那个 (self.dateOfCrawl)。

Answer 3

您可以通过这种方式访问​​此变量：

Site.dateOfCrawl

Static class variables in Python