How to replace the some characters from the end of a string?

Question

I want to replace characters at the end of a python string. I have this string:

 s = "123123" 

I want to replace the last 2 with x. Suppose there is a method called replace_last:

 r = replace_last(s, '2', 'x')  print r  1231x3 

Is there any built-in or easy method to do this?

Answer 1

This is exactly what the rpartition function is used for:

rpartition(...) S.rpartition(sep) -> (head, sep, tail)

Search for the separator sep in S, starting at the end of S, and return the part before it, the separator itself, and the part after it.  If the separator is not found, return two empty strings and S. 

I wrote this function showing how to use rpartition in your use case:

def replace_last(source_string, replace_what, replace_with):     head, _sep, tail = source_string.rpartition(replace_what)     return head + replace_with + tail  s = "123123" r = replace_last(s, '2', 'x') print r 

Output:

1231x3 

Answer 2

Using regular expression function re.sub to replace words at end of string

import re s = "123123" s = re.sub('23$', 'penguins', s) print s 

Prints:

1231penguins 

or

import re s = "123123" s = re.sub('^12', 'penguins', s) print s 

Prints:

penguins3123