Python正则表达式替换捕获

Question

I'm trying to add one space before and after +- , using re.sub (only) what expression to use?

import re

text = """a+b
a+b-c
a + b - c
a+b-c+d-e
a + b - c + d - e"""

text = re.sub('(\s?[+-]\s?)', r' \1 ', text)
print(text)

expected result:

a + b
a + b - c
a + b - c
a + b - c + d - e
a + b - c + d - e

 <script type="text/javascript" src="//cdn.datacamp.com/dcl-react.js.gz"></script> <div data-datacamp-exercise data-lang="python"> <code data-type="sample-code"> import re text = """a+b a+bc a + b - c a+b-c+de a + b - c + d - e """ text = re.sub('(\\s?[+-]\\s?)', r' \\1 ', text) print(text) </code> </div> 

Answer 1

Try capturing only the [+-] , and then replace with that group surrounded by spaces:

text = re.sub('\s?([+-])\s?', r' \1 ', text)

 <script type="text/javascript" src="//cdn.datacamp.com/dcl-react.js.gz"></script> <div data-datacamp-exercise data-lang="python"> <code data-type="sample-code"> import re text = """a+b a+bc a + b - c a+b-c+de a + b - c + d - e """ text = re.sub('\\s?([+-])\\s?', r' \\1 ', text) print(text) </code> </div> 

You also might consider repeating the \\s s with * instead of ? , so that, for example, 3 + 5 gets prettified to 3 + 5 :

\s*([+-])\s*

Answer 2

You can use a lambda function with re.sub :

import re
new_text = re.sub('(?<=\S)[\+\-](?=\S)', lambda x:f' {x.group()} ', text)

Output:

a + b
a + b - c
a + b - c
a + b - c + d - e
a + b - c + d - e