Replace nth occurrence of substring in string

Question

I want to replace the n\'th occurrence of a substring in a string.

There\'s got to be something equivalent to what I WANT to do which is

mystring.repl

Answer 1

General solution: replace any specified instance(s) of a substring [pattern] with another string.

def replace(instring,pattern,replacement,n=[1]):
  """Replace specified instance(s) of pattern in string.

  Positional arguments
    instring - input string
     pattern - regular expression pattern to search for
 replacement - replacement

  Keyword arguments
           n - list of instances requested to be replaced [default [1]]

"""
  import re
  outstring=''
  i=0
  for j,m in enumerate(re.finditer(pattern,instring)):
    if j+1 in n: outstring+=instring[i:m.start()]+replacement
    else: outstring+=instring[i:m.end()]
    i=m.end()
  outstring+=instring[i:]
  return outstring