How to apply a function on a backreference?

Question

Say I have strings like the following:

old_string = \"I love the number 3 so much\"

I would like to spot the integer numbers (in the exampl

Answer 1

In addition to having a replace string, re.sub allows you to use a function to do the replacements:

>>> import re
>>> old_string = "I love the number 3 so much"
>>> def f(match):
...     return str(int(match.group(1)) + 1)
...
>>> re.sub('([0-9])+', f, old_string)
'I love the number 4 so much'
>>>

From the docs:

re.sub(pattern, repl, string, count=0, flags=0)

If repl is a function, it is called for every non-overlapping occurrence of pattern. The function takes a single match object argument, and returns the replacement string.