Python - 全局變量未定義（但它是）

Question

所以我正在處理這個文件，將CSV轉換爲JSON，但是我不斷收到此錯誤消息，但似乎無法弄清楚。縮進似乎是正確的，所以我有點失落在哪裏去。代碼如下：

回溯（最新最後調用）：

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 

代碼

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

分配dateOfCrawl = 0;（請閱讀PEP-8）作爲類屬性。出於某種原因，您也在混合global，這是完全分開的。它不是很清楚爲什麼dateOfCrawl應該是一個類（而不是實例）屬性，或爲什麼你也有global。你或許應該只是：

1. 讓它的實例屬性（移動dateOfCrawl = 0內__init__）;那麼
2. 接入即其他方法（self.dateOfCrawl）。

Answer 2

您需要定義global dateOfCrawl。移動dateOfCrawl = 0;內Site類__init__，是這樣的：

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

Answer 3

你可以訪問此變量是這樣的：

Site.dateOfCrawl 

Static class variables in Python