如何在python中将字符串中的相同字符更改为不同的值？

Question

我正在尝试实现一个基本的转换程序，根据它们是一对中的第一颗还是第二颗，将恒星更改为<em>或</em> ，但是无论我做什么，我的程序都会将所有恒星更改为<em>或</em> 。

line = "*ju*bil*ee*"
star_counter = 0
new_line = line
    for character in line:
         if character is "*":
            star_counter += 1
            if star_counter%2 == 0:
                new_line = line.replace(character, "</em>")
            else:
                new_line = line.replace(character, "<em>")

Answer 1

您已经在逐个字符地循环输入字符串，因此只需追加到输出即可（打开/关闭em标签的切换是可以的）。

line = "*ju*bil*ee*"
expected = "<em>ju</em>bil<em>ee</em>"
star_counter = 0
new_line = ""
for character in line:
  if character is "*":
    star_counter += 1
    if star_counter%2 == 0:
      new_line += "</em>"
    else:
      new_line += "<em>"
  else:
    new_line += character

assert new_line == expected

Answer 2

使用来自itertools cycle和imap解决方案：

from itertools import cycle, imap

em = iter(cycle(['<em>','</em>']))

def emEm(c):
    if c == '*':
        return em.next() 
    else:
       return c

line = imap(emEm,"*ju*bil*ee*") 
print(''.join(line)) 

• cycle(['<em>','</em>'])视需要懒惰地重复<em>和</em>
• emEm为imap实现了emEm逻辑
• imap对字符串的每个字符执行逻辑

问题：*为奇数时，您会得到格式不正确的html-标签会打开但不会关闭-但您可以事先检查。

Answer 3

new_line = "*ju*bil*ee*"
star_counter = 0
for character in new_line:
    if character is "*":
        if star_counter == 0:
            new_line = new_line.replace(character, "<em>", 1)
            star_counter=1
        else:
            new_line = new_line.replace(character, "</em>", 1)
            star_counter = 0
print(new_line)

输出量

<em>ju</em>bil<em>ee</em>

Answer 4

您可以使用正则表达式替换来执行此操作。

import re
new_line = re.sub(r'\*([^*]+)\*', r'<em>\1</em>', line)

正则表达式将两个*匹配，它们之间有一些非*字符，使用捕获组捕获中间的文本，然后在结果中的<em>和</em>之间替换该捕获组。