Python - > TypeError：list indices必须是整数，而不是str

Question

我在python中有一个list / array str4，我想用变量访问它，我强烈认为它是一个int，因为我用函数isdigit（）测试它，我也进行了手动调试并检查所有选项是否出来正确的唯一号码。

temp = "variableX"
file2 = open('file.txt','r')
for line in file2:
  if line.find(temp) =! -1:
    posArray = line.split(temp)[1][1:3]
    if ")" in posArray:
      posArray = posArray[:-1]
    if posArray.isdigit():
      num = posArray
      print temp+"("+num+")"
      print num
      print str4[num]

上面的代码用于调试，我的问题是在str4 [num]中，上面代码的结果是：

variableX(1)
1
"this is position 1"
Traceback (most recent call last):
  File "orderList.py", line34, in <module>
    print str4[num]
TypeError: list indices must be integers, not str

为什么num是一个数字，但python告诉我它是一个字符串？我究竟做错了什么？

Answer 1

翻译永远不会错......

更严重的是，您将num作为子字符串，因此它是一个字符串。如果要将其用作字符串索引，则必须将其转换为int：

  num = int(posArray)          # ok num is now an int
  print temp+"("+str(num)+")"  # must use str to concat it with strings
  print num, type(num), posArray, type(posArray) # num is int, posArray is string
  print str4[num]              # now fine

Answer 2

您检查字符串posArray是否为数字：

  if posArray.isdigit():
      num = posArray

但你没有把它转换成数字，就像这样：

  if posArray.isdigit():
      num = int(posArray)

Answer 3

请查看下面的评论，查看您的代码。从底部到顶部阅读它，以了解如何轻松调试自己的代码;思考过程是什么。

temp = "variableX"
file2 = open('file.txt','r')  # which is a file, so `line` is `string` - CASE CLOSED
for line in file2:  # and `line` is a result of looping through `file2`
  if line.find(temp) =! -1:
    posArray = line.split(temp)[1][1:3]  # and `posArray` is a part of `line`
    if ")" in posArray:
      posArray = posArray[:-1]  # ok, `posArray` is a part of `posArray`
    if posArray.isdigit():  # `posArray` contains digits only but that doesn't help really, so does "123"..
      num = posArray  # ok, so `num` is whatever `posArray` is
      print temp+"("+num+")"
      print num
      print str4[num]  # here is the Error so we start here and work backwards

我们上面显示的是，最终，num将与line（str）属于同一类型，因此，不能用于index任何东西。它必须首先通过int转换为int(num)

Answer 4

另一个解决方案是

num = posArray

做：

print str4[int(num)])