与re.sub混淆

Question

I have the string aa{{{a {{ {aaa{ that I would like to translate to aa { { {a { { {aaa { . Basically every { must a space character before it.

My regular expression substitution function I am currently using is: re.sub(r'[^\\ ]{', lambda x:x.group(0)[0]+' {', test_case) The result from the function is: aa {{ {a { { {aaa { (Close, but there is a {{ in the string)

My method performs very well on section like a{a{a . However if two { characters are together like a{{a it only seems to operate on the first { and completely neglect the following { .

A more clear example will be a large series of {{{{{{{{{{{{ . My regex substitution returns: { {{ {{ {{ {{ {{ { . Which clearly skips over every other character given tightly nested { .

Why are they skipping? Any help to untangle this confusion would be greatly appreciated!

PS I am sorry to everyone out there that have the strong desire to close all the opened curly-brace.

Answer 1

I'd use a negative lookbehind:

re.sub(r'(?<!\s)(\{)',r' \1','{{{{{{')

Basically we parse the string until we hit a { . If the character before it isn't whitespace (that's the (?<!\\s) bit), the { matches and we replace it with a space in front.

Answer 2

They are skipping because your regular expression is consuming two characters: [^\\ ] and { . You need to use 0-width negative lookbehind for the preceding space in order not to consume it: (?!<\\s){ . Then you can just replace it with " {" , without the lambda hassle.

Answer 3

我希望这可以解决问题：

re.sub (' *{', ' {', test_case)