Python：得到了“分配前引用的局部變量‘idx’”的錯誤語句

Question

def removeNonAlpha(myString, key):
      from string import ascii_lowercase
      alphabet = ascii_lowercase + ' '
      myString = myString.lower()
      cipherText = ' '
      for ch in myString:
        if ch == 1 or ch == 2 or ch == 3 or ch == 4 or ch == 5 or ch == 6 or ch == 7 or ch == 8 or ch == 9 :
          idx = alphabet.find(ch)
        cipherText = cipherText + key[idx] 
      return cipherText

運行我的腳本：

removeNonAlpha('My favorite Cat was named Patches', alphabet)

返回以下錯誤

          7     if ch == 1 or ch == 2 or ch == 3 or ch == 4 or ch == 5 or ch == 6 or ch == 7 or ch == 8 or ch == 9 :
          8       idx = alphabet.find(idx)
    ----> 9     cipherText = cipherText + key[idx]
         10   return cipherText

UnboundLocalError: local variable 'idx' referenced before assignment

我的代碼有什么問題？

Answer 1

這意味着您在創建之前嘗試使用變量“idx”。 'idx' 僅在 if 內部創建，但使用 'idx' 的行在 'if' 語句之外，因此即使在 'if' 失敗時它也會運行

Answer 2

只需將功能更改為以下內容：

def removeNonAlpha(myString, key):
  from string import ascii_lowercase
  alphabet = ascii_lowercase + ' '
  myString = myString.lower()
  cipherText = ' '
  for ch in myString:
    if ch == 1 or ch == 2 or ch == 3 or ch == 4 or ch == 5 or ch == 6 or ch == 7 or ch == 8 or ch == 9 :
      idx = alphabet.find(ch)
      cipherText = cipherText + key[idx] #edits
  return cipherText

Answer 3

這是因為如果條件未通過，則您的 idx 未初始化，此外，您可以對大量條件進行一些更改，請嘗試以下操作：

def removeNonAlpha(myString, key):
      from string import ascii_lowercase
      alphabet = ascii_lowercase + ' '
      myString = myString.lower()
      cipherText = ' '
      for ch in myString:
        idx = #make some default value 
        if ch in ['123456789']:
          idx = alphabet.find(ch)
        cipherText = cipherText + key[idx] 
      return cipherText

您必須使用一些默認值初始化 idx 並且可以添加檢查是否找到 idx 。

Answer 4

更新：完全改變了我的代碼，但這是工作結果：

`def removeNonAlpha(myString):
  from string import ascii_lowercase
  alphabet = ascii_lowercase + ' '
  myString = myString.lower()
  cipherText = ' '
  

  return myString


def getFreq(tuples): 
  return tuples[1]
  # this returns the second element of a tuple #
countDict = {}
with open('wells.txt', 'r', encoding='utf-8') as wells:
  text = wells.read()
  for word in text.split():
    word = removeNonAlpha(word)
    if word in countDict:
      countDict[word] += 1
    else: 
      countDict[word] = 1


wordList = list(countDict.items())

wordList.sort(key = getFreq)

for wordTuple in wordList[-10:]:
  print(wordTuple)`