What's the most pythonic way to apply a function on every word in a string with multiple types of white space characters?

Question

Suppose I have a function

def f(a):
  return a[::-1]

I want to apply the function f to every word on a string. If the string consists only of s

Answer 1

Use a regular expression, the re.sub() function accepts a function to do the substitutions. Match non-whitespace instead:

re.sub(r'[^\s]+', lambda m: f(m.group(0)), s)

The function is passed a match object; using .group(0) you can extract the matched text to pass it to your function. The return value is used to replace the original matched text in the output string.

Demo:

>>> import re
>>> def f(a):
...   return a[::-1]
...
>>> s = '\t  \t this  is a\tbanana   \n'
>>> re.sub(r'[^\s]+', lambda m: f(m.group(0)), s)
'\t  \t siht  si a\tananab   \n'