Passing a function to re.sub in Python

Question

I have strings that contain a number somewhere in them and I'm trying to replace this number with their word notation (ie. 3 -> three). I have a function that does this. The problem now is finding the number inside the string, while keeping the rest of the string intact. For this, I opted to use the re.sub function, which can accept a "callable". However, the object passed to it is the internal _sre.SRE_Match and I'm not sure how to handle it. My function accepts a number or its string representation.

How should I write some helper function which can be used to bridge the re.sub call with my function doing the required processing? Alternatively, is there a better way to do what I want?

Answer 1

You should call group() to get the matching string:

import re  number_mapping = {'1': 'one',                   '2': 'two',                   '3': 'three'} s = "1 testing 2 3"  print re.sub(r'\d', lambda x: number_mapping[x.group()], s) 

prints:

one testing two three