How To Replace Only The Contents Within Brackets Using Regular Expressions?

How to replace only the contents within brackets using regular expressions? String = 'This is my string [123]' I want to replace 123 with 456 Desired_String = 'This is my string [

Solution 1:

If you modify your regex and your replacement string a little, you get it:

regex = '\[.*?\]'
re.sub(regex,'[456]',String)

You don't need to match the entire string with .* for the substitution to work.

Also, it's not entirely required here, but it's good practice to raw your regex strings:

regex = r'\[.*?\]'
        ^

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Another option would be to use negated classes, which will be faster as well!

regex = r'[^\[\]]+(?=\])'
re.sub(regex,'456',String)

It might be a little confusing, but [^\[\]]+ matches any character except [ and ].

regex101 demo

Solution 2:

Alternatively, you could use look-ahead and look-behind assertions (documentation):

>>>regex = r'(?<=\[).*?(?=\])'>>>re.sub(regex, '456', 'This is my string [123]')
'This is my string [456]'