使用一下上节课的芝士，这么久都没敢发过自己的代码

Discuss / Python / 使用一下上节课的芝士，这么久都没敢发过自己的代码

Back

Topic source

#1 Created at ... [Delete] [Delete and Lock User]

#!/usr/bin/pystu python3

# -*- coding: utf-8 -*-

def trim(s):

if s == '':

return s

elif s[0] == ' ':

s = trim(s[1:])

elif s[-1] == ' ':

s = trim(s[:-2])

return s

#2 Created at ... [Delete] [Delete and Lock User]

elif s[-1] == ' ':

s = trim(s[:-2])

请教一下这两行代码里面为什么s = trim(s[:-2])或者s = trim(s[:-1])都可以测试成功

#3 Created at ... [Delete] [Delete and Lock User]

你这个厉害了! 几行递归小程序就解决了.

#4 Created at ... [Delete] [Delete and Lock User]

去掉收尾空格还是正则简单

def trim(s):    import re    re_s=re.compile(r'^\s+|\s+$')    return re.sub(re_s,'',s)

#5 Created at ... [Delete] [Delete and Lock User]

那如果s【0】==‘’ ，s【-1】==‘’同时存在呢

#6 Created at ... [Delete] [Delete and Lock User]

倒数第二行应该是：s = trim(s[:-1])，s[:-1]是不包含索引-1的

#7 Created at ... [Delete] [Delete and Lock User]

有一个疑问，if语句不是由上向下执行的吗，那么如果我是首尾都空格，我在满足第二个条件后应该退出，返回的函数值在尾部应该还有一个空格，为什么这个首尾都能去掉啊，是我理解错了吗

#8 Created at ... [Delete] [Delete and Lock User]

楼上，他这个是递归，

 elif s[0] == ' ':
     s = trim(s[1:])

这个就表示如果字符串首为空格，就截取第二个开始到最后，然后重新调用该方法`trim`，如果尾部有空格就会进入第二个 `elis`去除尾部空格。直到首尾都没有空格

#9 Created at ... [Delete] [Delete and Lock User]

测试了一下这个是有问题的，

 elif s[-1] == ' ':
         s = trim(s[:-2])

这部分代码，当字符串尾部有奇数个空格就会多截取一个,因为切片操作是左开右闭，即 [:-2]其实是倒是第二个元素不会被切片操作截取在内，比如a = [1,2,3,4] ,a[:-2]结果是[1,2]，所以这里应该改为

elif s[-1] == ' ':
         s = trim(s[:-1])  // 将s[:-2]改为s[:-1]