TypeError:“in<string>”需要string作为左操作数，而不是in

Question

为什么在最基本的Python脚本中会出现这个错误？这个错误是什么意思？

错误：

Traceback (most recent call last):
  File "cab.py", line 16, in <module>
    if cab in line:
TypeError: 'in <string>' requires string as left operand, not int

脚本：

import re
import sys

#loco = sys.argv[1]
cab = 6176
fileZ = open('cabs.txt')
fileZ = list(set(fileZ))

for line in fileZ:
     if cab in line: 
        IPaddr = (line.strip().split())
        print(IPaddr[4])

Answer 1

您只需将cab设为一个字符串：

cab = '6176'

如错误消息所述，您不能执行<int> in <string>：

>>> 1 in '123'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'in <string>' requires string as left operand, not int
>>> 

因为integers和strings是两个完全不同的东西，Python不接受隐式类型转换（"Explicit is better than implicit."）。

实际上，如果左操作数也是string类型，Python只允许您对string类型的右操作数使用in运算符：

>>> '1' in '123'  # Works!
True
>>>
>>> [] in '123'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'in <string>' requires string as left operand, not list
>>>
>>> 1.0 in '123'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'in <string>' requires string as left operand, not float
>>>
>>> {} in '123'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'in <string>' requires string as left operand, not dict
>>>