学习Python并尝试获取字符串的前两个字母和后两个字母

Question

这是我的代码：

# B. both_ends
# Given a string s, return a string made of the first 2
# and the last 2 chars of the original string,
# so 'spring' yields 'spng'. However, if the string length
# is less than 2, return instead the empty string.
def both_ends(s):
  if len(s) <= 2:
    return ""
  else:
    return s[0] + s[1] + s[len(s)-2] + s[len(s-1)]
  # +++your code here+++
  return

不幸的是我的程序没有运行。（我肯定我是个学Python的新手，所以我忽略了一些东西。

错误如下：

> Traceback (most recent call last):
  File "C:\Users\Sergio\Desktop\google-python-exercises\google-python-exercises\basic\string1.py", line 120, in <module>
    main()
  File "C:\Users\Sergio\Desktop\google-python-exercises\google-python-exercises\basic\string1.py", line 97, in main
    test(both_ends('spring'), 'spng')
  File "C:\Users\Sergio\Desktop\google-python-exercises\google-python-exercises\basic\string1.py", line 44, in both_ends
    return s[0] + s[1] + s[len(s)-2] + s[len(s-1)]
TypeError: unsupported operand type(s) for -: 'str' and 'int'

谢谢你们的帮助。：天

Answer 1

最后一部分出错：

return s[0] + s[1] + s[len(s)-2] + s[len(s)-1]

你可以考虑用一种更像Python的方式重写它：

return s[0] + s[1] + s[-2] + s[-1]

Answer 2

你眼前的问题是s[len(s-1)]，而不是s[len(s)-1]。

您也可以简化为s[:2] + s[-2:]。

Answer 3

括号放错位置：

return s[0] + s[1] + s[len(s)-2] + s[len(s)-1]

顺便说一句：

return s[0] + s[1] + s[-2] + s[-1]

或者

return s[:2] + s[-2:]