使用Python正则表达式删除匹配的括号

Question

我有一个Latex文件，里面有很多文字是用\red{}标记的，但在\red{}里面可能还会有括号，比如\red{here is \underline{underlined} text}。我想去掉红色的标记，经过一些搜索，我写了这个Python脚本：

import os, re, sys
#Start program in terminal with
#python RedRemover.py filename
#sys.argv[1] then has the value filename
ifn = sys.argv[1]
#Open file and read it
f = open(ifn, "r")
c = f.read() 
#The whole file content is now stored in the string c
#Remove occurences of \red{...} in c
c=re.sub(r'\\red\{(?:[^\}|]*\|)?([^\}|]*)\}', r'\1', c)
#Write c into new file
Nf=open("RedRemoved_"+ifn,"w")
Nf.write(c)

f.close()
Nf.close()

但是这个脚本会把

\red{here is \underline{underlined} text}

转换成

here is \underline{underlined text}

这不是我想要的。我想要的是

here is \underline{underlined} text

Answer 1

我觉得你需要保留大括号，看看这个例子：\red{\bf test}：

import re

c = r'\red{here is \underline{underlined} text} and \red{more}'
d = c 

# this may be less painful and sufficient, and even more correct
c = re.sub(r'\\red\b', r'', c)
print "1ST:", c

# if you want to get rid of the curlies:
d = re.sub(r'\\red{([^{]*(?:{[^}]*}[^}]*)*)}', r'\1', d)
print "2ND:", d

结果是：

1ST: {here is \underline{underlined} text} and {more}
2ND: here is \underline{underlined} text and more

Answer 2

你无法用re模块来匹配不确定层数的嵌套括号，因为它不支持递归。要解决这个问题，你可以使用新的regex模块：

import regex

c = r'\red{here is \underline{underlined} text}'

c = regex.sub(r'\\red({((?>[^{}]+|(?1))*)})', r'\2', c)

这里的(?1)是对捕获组1的递归调用。