Is there an equivalent of $` in Javascript's `replace()` for Python's re.sub()?

Question

In JS , you can use

• $` Inserts the portion of the string that precedes the matched substring.

• $' Inserts the portion of the string that follows the matched substring.

To get the substring before and after the match.

Is there an equivalent of this in Python's re.sub() ?

Answer 1

Instead of a replacement string, you can pass a function to re.sub . The function will receive a match object, and should return the replacement for the match.

Within the function, you can use match.start() and match.end() to get the start and end indices of the match in the original string, andmatch.string to get the original string passed to re.sub . Thus,

match.string[:match.start()]

gives the effect of $` , and

match.string[match.end():]

gives the effect of $' .